1//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This pass transforms simple global variables that never have their address
10// taken. If obviously true, it marks read/write globals as constant, deletes
11// variables only stored to, etc.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/IPO/GlobalOpt.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/ADT/Twine.h"
22#include "llvm/ADT/iterator_range.h"
23#include "llvm/Analysis/BlockFrequencyInfo.h"
24#include "llvm/Analysis/ConstantFolding.h"
25#include "llvm/Analysis/MemoryBuiltins.h"
26#include "llvm/Analysis/TargetLibraryInfo.h"
27#include "llvm/Analysis/TargetTransformInfo.h"
28#include "llvm/Analysis/ValueTracking.h"
29#include "llvm/BinaryFormat/Dwarf.h"
30#include "llvm/IR/Attributes.h"
31#include "llvm/IR/BasicBlock.h"
32#include "llvm/IR/CallingConv.h"
33#include "llvm/IR/Constant.h"
34#include "llvm/IR/Constants.h"
35#include "llvm/IR/DataLayout.h"
36#include "llvm/IR/DebugInfoMetadata.h"
37#include "llvm/IR/DerivedTypes.h"
38#include "llvm/IR/Dominators.h"
39#include "llvm/IR/Function.h"
40#include "llvm/IR/GlobalAlias.h"
41#include "llvm/IR/GlobalValue.h"
42#include "llvm/IR/GlobalVariable.h"
43#include "llvm/IR/IRBuilder.h"
44#include "llvm/IR/InstrTypes.h"
45#include "llvm/IR/Instruction.h"
46#include "llvm/IR/Instructions.h"
47#include "llvm/IR/IntrinsicInst.h"
48#include "llvm/IR/Module.h"
49#include "llvm/IR/Operator.h"
50#include "llvm/IR/ProfDataUtils.h"
51#include "llvm/IR/Type.h"
52#include "llvm/IR/Use.h"
53#include "llvm/IR/User.h"
54#include "llvm/IR/Value.h"
55#include "llvm/IR/ValueHandle.h"
56#include "llvm/Support/AtomicOrdering.h"
57#include "llvm/Support/Casting.h"
58#include "llvm/Support/CommandLine.h"
59#include "llvm/Support/Debug.h"
60#include "llvm/Support/ErrorHandling.h"
61#include "llvm/Support/raw_ostream.h"
62#include "llvm/Transforms/IPO.h"
63#include "llvm/Transforms/Utils/CtorUtils.h"
64#include "llvm/Transforms/Utils/Evaluator.h"
65#include "llvm/Transforms/Utils/GlobalStatus.h"
66#include "llvm/Transforms/Utils/Local.h"
67#include <cassert>
68#include <cstdint>
69#include <optional>
70#include <utility>
71#include <vector>
72
73using namespace llvm;
74
75#define DEBUG_TYPE "globalopt"
76
77STATISTIC(NumMarked , "Number of globals marked constant");
78STATISTIC(NumUnnamed , "Number of globals marked unnamed_addr");
79STATISTIC(NumSRA , "Number of aggregate globals broken into scalars");
80STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
81STATISTIC(NumDeleted , "Number of globals deleted");
82STATISTIC(NumGlobUses , "Number of global uses devirtualized");
83STATISTIC(NumLocalized , "Number of globals localized");
84STATISTIC(NumShrunkToBool , "Number of global vars shrunk to booleans");
85STATISTIC(NumFastCallFns , "Number of functions converted to fastcc");
86STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
87STATISTIC(NumNestRemoved , "Number of nest attributes removed");
88STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
89STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
90STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
91STATISTIC(NumAtExitRemoved, "Number of atexit handlers removed");
92STATISTIC(NumInternalFunc, "Number of internal functions");
93STATISTIC(NumColdCC, "Number of functions marked coldcc");
94STATISTIC(NumIFuncsResolved, "Number of statically resolved IFuncs");
95STATISTIC(NumIFuncsDeleted, "Number of IFuncs removed");
96
97static cl::opt<bool>
98 OptimizeNonFMVCallers("optimize-non-fmv-callers",
99 cl::desc("Statically resolve calls to versioned "
100 "functions from non-versioned callers."),
101 cl::init(Val: true), cl::Hidden);
102
103static cl::opt<unsigned> MaxIFuncVersions(
104 "max-ifunc-versions", cl::Hidden, cl::init(Val: 5),
105 cl::desc("Maximum number of caller/callee versions that is allowed for "
106 "using the expensive (cubic) static resolution algorithm."));
107
108static cl::opt<bool>
109 EnableColdCCStressTest("enable-coldcc-stress-test",
110 cl::desc("Enable stress test of coldcc by adding "
111 "calling conv to all internal functions."),
112 cl::init(Val: false), cl::Hidden);
113
114static cl::opt<int> ColdCCRelFreq(
115 "coldcc-rel-freq", cl::Hidden, cl::init(Val: 2),
116 cl::desc(
117 "Maximum block frequency, expressed as a percentage of caller's "
118 "entry frequency, for a call site to be considered cold for enabling "
119 "coldcc"));
120
121/// Is this global variable possibly used by a leak checker as a root? If so,
122/// we might not really want to eliminate the stores to it.
123static bool isLeakCheckerRoot(GlobalVariable *GV) {
124 // A global variable is a root if it is a pointer, or could plausibly contain
125 // a pointer. There are two challenges; one is that we could have a struct
126 // the has an inner member which is a pointer. We recurse through the type to
127 // detect these (up to a point). The other is that we may actually be a union
128 // of a pointer and another type, and so our LLVM type is an integer which
129 // gets converted into a pointer, or our type is an [i8 x #] with a pointer
130 // potentially contained here.
131
132 if (GV->hasPrivateLinkage())
133 return false;
134
135 SmallVector<Type *, 4> Types;
136 Types.push_back(Elt: GV->getValueType());
137
138 unsigned Limit = 20;
139 do {
140 Type *Ty = Types.pop_back_val();
141 switch (Ty->getTypeID()) {
142 default: break;
143 case Type::PointerTyID:
144 return true;
145 case Type::FixedVectorTyID:
146 case Type::ScalableVectorTyID:
147 if (cast<VectorType>(Val: Ty)->getElementType()->isPointerTy())
148 return true;
149 break;
150 case Type::ArrayTyID:
151 Types.push_back(Elt: cast<ArrayType>(Val: Ty)->getElementType());
152 break;
153 case Type::StructTyID: {
154 StructType *STy = cast<StructType>(Val: Ty);
155 if (STy->isOpaque()) return true;
156 for (Type *InnerTy : STy->elements()) {
157 if (isa<PointerType>(Val: InnerTy)) return true;
158 if (isa<StructType>(Val: InnerTy) || isa<ArrayType>(Val: InnerTy) ||
159 isa<VectorType>(Val: InnerTy))
160 Types.push_back(Elt: InnerTy);
161 }
162 break;
163 }
164 }
165 if (--Limit == 0) return true;
166 } while (!Types.empty());
167 return false;
168}
169
170/// Given a value that is stored to a global but never read, determine whether
171/// it's safe to remove the store and the chain of computation that feeds the
172/// store.
173static bool IsSafeComputationToRemove(
174 Value *V, function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
175 do {
176 if (isa<Constant>(Val: V))
177 return true;
178 if (!V->hasOneUse())
179 return false;
180 if (isa<LoadInst>(Val: V) || isa<InvokeInst>(Val: V) || isa<Argument>(Val: V) ||
181 isa<GlobalValue>(Val: V))
182 return false;
183 if (isAllocationFn(V, GetTLI))
184 return true;
185
186 Instruction *I = cast<Instruction>(Val: V);
187 if (I->mayHaveSideEffects())
188 return false;
189 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Val: I)) {
190 if (!GEP->hasAllConstantIndices())
191 return false;
192 } else if (I->getNumOperands() != 1) {
193 return false;
194 }
195
196 V = I->getOperand(i: 0);
197 } while (true);
198}
199
200/// This GV is a pointer root. Loop over all users of the global and clean up
201/// any that obviously don't assign the global a value that isn't dynamically
202/// allocated.
203static bool
204CleanupPointerRootUsers(GlobalVariable *GV,
205 function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
206 // A brief explanation of leak checkers. The goal is to find bugs where
207 // pointers are forgotten, causing an accumulating growth in memory
208 // usage over time. The common strategy for leak checkers is to explicitly
209 // allow the memory pointed to by globals at exit. This is popular because it
210 // also solves another problem where the main thread of a C++ program may shut
211 // down before other threads that are still expecting to use those globals. To
212 // handle that case, we expect the program may create a singleton and never
213 // destroy it.
214
215 bool Changed = false;
216
217 // If Dead[n].first is the only use of a malloc result, we can delete its
218 // chain of computation and the store to the global in Dead[n].second.
219 SmallVector<std::pair<Instruction *, Instruction *>, 32> Dead;
220
221 SmallVector<User *> Worklist(GV->users());
222 // Constants can't be pointers to dynamically allocated memory.
223 while (!Worklist.empty()) {
224 User *U = Worklist.pop_back_val();
225 if (StoreInst *SI = dyn_cast<StoreInst>(Val: U)) {
226 Value *V = SI->getValueOperand();
227 if (isa<Constant>(Val: V)) {
228 Changed = true;
229 SI->eraseFromParent();
230 } else if (Instruction *I = dyn_cast<Instruction>(Val: V)) {
231 if (I->hasOneUse())
232 Dead.push_back(Elt: std::make_pair(x&: I, y&: SI));
233 }
234 } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(Val: U)) {
235 if (isa<Constant>(Val: MSI->getValue())) {
236 Changed = true;
237 MSI->eraseFromParent();
238 } else if (Instruction *I = dyn_cast<Instruction>(Val: MSI->getValue())) {
239 if (I->hasOneUse())
240 Dead.push_back(Elt: std::make_pair(x&: I, y&: MSI));
241 }
242 } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(Val: U)) {
243 GlobalVariable *MemSrc = dyn_cast<GlobalVariable>(Val: MTI->getSource());
244 if (MemSrc && MemSrc->isConstant()) {
245 Changed = true;
246 MTI->eraseFromParent();
247 } else if (Instruction *I = dyn_cast<Instruction>(Val: MTI->getSource())) {
248 if (I->hasOneUse())
249 Dead.push_back(Elt: std::make_pair(x&: I, y&: MTI));
250 }
251 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Val: U)) {
252 if (isa<GEPOperator>(Val: CE))
253 append_range(C&: Worklist, R: CE->users());
254 }
255 }
256
257 for (const auto &[Inst, Store] : Dead) {
258 if (IsSafeComputationToRemove(V: Inst, GetTLI)) {
259 Store->eraseFromParent();
260 Instruction *I = Inst;
261 do {
262 if (isAllocationFn(V: I, GetTLI))
263 break;
264 Instruction *J = dyn_cast<Instruction>(Val: I->getOperand(i: 0));
265 if (!J)
266 break;
267 I->eraseFromParent();
268 I = J;
269 } while (true);
270 I->eraseFromParent();
271 Changed = true;
272 }
273 }
274
275 GV->removeDeadConstantUsers();
276 return Changed;
277}
278
279/// We just marked GV constant. Loop over all users of the global, cleaning up
280/// the obvious ones. This is largely just a quick scan over the use list to
281/// clean up the easy and obvious cruft. This returns true if it made a change.
282static bool CleanupConstantGlobalUsers(GlobalVariable *GV,
283 const DataLayout &DL) {
284 Constant *Init = GV->getInitializer();
285 SmallVector<User *, 8> WorkList(GV->users());
286 SmallPtrSet<User *, 8> Visited;
287 bool Changed = false;
288
289 SmallVector<WeakTrackingVH> MaybeDeadInsts;
290 auto EraseFromParent = [&](Instruction *I) {
291 for (Value *Op : I->operands())
292 if (auto *OpI = dyn_cast<Instruction>(Val: Op))
293 MaybeDeadInsts.push_back(Elt: OpI);
294 I->eraseFromParent();
295 Changed = true;
296 };
297 while (!WorkList.empty()) {
298 User *U = WorkList.pop_back_val();
299 if (!Visited.insert(Ptr: U).second)
300 continue;
301
302 if (auto *BO = dyn_cast<BitCastOperator>(Val: U))
303 append_range(C&: WorkList, R: BO->users());
304 if (auto *ASC = dyn_cast<AddrSpaceCastOperator>(Val: U))
305 append_range(C&: WorkList, R: ASC->users());
306 else if (auto *GEP = dyn_cast<GEPOperator>(Val: U))
307 append_range(C&: WorkList, R: GEP->users());
308 else if (auto *LI = dyn_cast<LoadInst>(Val: U)) {
309 // A load from a uniform value is always the same, regardless of any
310 // applied offset.
311 Type *Ty = LI->getType();
312 if (Constant *Res = ConstantFoldLoadFromUniformValue(C: Init, Ty, DL)) {
313 LI->replaceAllUsesWith(V: Res);
314 EraseFromParent(LI);
315 continue;
316 }
317
318 Value *PtrOp = LI->getPointerOperand();
319 APInt Offset(DL.getIndexTypeSizeInBits(Ty: PtrOp->getType()), 0);
320 PtrOp = PtrOp->stripAndAccumulateConstantOffsets(
321 DL, Offset, /* AllowNonInbounds */ true);
322 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Val: PtrOp)) {
323 if (II->getIntrinsicID() == Intrinsic::threadlocal_address)
324 PtrOp = II->getArgOperand(i: 0);
325 }
326 if (PtrOp == GV) {
327 if (auto *Value = ConstantFoldLoadFromConst(C: Init, Ty, Offset, DL)) {
328 LI->replaceAllUsesWith(V: Value);
329 EraseFromParent(LI);
330 }
331 }
332 } else if (StoreInst *SI = dyn_cast<StoreInst>(Val: U)) {
333 // Store must be unreachable or storing Init into the global.
334 EraseFromParent(SI);
335 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(Val: U)) { // memset/cpy/mv
336 if (getUnderlyingObject(V: MI->getRawDest()) == GV)
337 EraseFromParent(MI);
338 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Val: U)) {
339 if (II->getIntrinsicID() == Intrinsic::threadlocal_address)
340 append_range(C&: WorkList, R: II->users());
341 }
342 }
343
344 Changed |=
345 RecursivelyDeleteTriviallyDeadInstructionsPermissive(DeadInsts&: MaybeDeadInsts);
346 GV->removeDeadConstantUsers();
347 return Changed;
348}
349
350/// Part of the global at a specific offset, which is only accessed through
351/// loads and stores with the given type.
352struct GlobalPart {
353 Type *Ty;
354 Constant *Initializer = nullptr;
355 bool IsLoaded = false;
356 bool IsStored = false;
357};
358
359/// Look at all uses of the global and determine which (offset, type) pairs it
360/// can be split into.
361static bool collectSRATypes(DenseMap<uint64_t, GlobalPart> &Parts,
362 GlobalVariable *GV, const DataLayout &DL) {
363 SmallVector<Use *, 16> Worklist;
364 SmallPtrSet<Use *, 16> Visited;
365 auto AppendUses = [&](Value *V) {
366 for (Use &U : V->uses())
367 if (Visited.insert(Ptr: &U).second)
368 Worklist.push_back(Elt: &U);
369 };
370 AppendUses(GV);
371 while (!Worklist.empty()) {
372 Use *U = Worklist.pop_back_val();
373 User *V = U->getUser();
374
375 auto *GEP = dyn_cast<GEPOperator>(Val: V);
376 if (isa<BitCastOperator>(Val: V) || isa<AddrSpaceCastOperator>(Val: V) ||
377 (GEP && GEP->hasAllConstantIndices())) {
378 AppendUses(V);
379 continue;
380 }
381
382 if (Value *Ptr = getLoadStorePointerOperand(V)) {
383 // This is storing the global address into somewhere, not storing into
384 // the global.
385 if (isa<StoreInst>(Val: V) && U->getOperandNo() == 0)
386 return false;
387
388 APInt Offset(DL.getIndexTypeSizeInBits(Ty: Ptr->getType()), 0);
389 Ptr = Ptr->stripAndAccumulateConstantOffsets(DL, Offset,
390 /* AllowNonInbounds */ true);
391 if (Ptr != GV || Offset.getActiveBits() >= 64)
392 return false;
393
394 // TODO: We currently require that all accesses at a given offset must
395 // use the same type. This could be relaxed.
396 Type *Ty = getLoadStoreType(I: V);
397 const auto &[It, Inserted] =
398 Parts.try_emplace(Key: Offset.getZExtValue(), Args: GlobalPart{.Ty: Ty});
399 if (Ty != It->second.Ty)
400 return false;
401
402 if (Inserted) {
403 It->second.Initializer =
404 ConstantFoldLoadFromConst(C: GV->getInitializer(), Ty, Offset, DL);
405 if (!It->second.Initializer) {
406 LLVM_DEBUG(dbgs() << "Global SRA: Failed to evaluate initializer of "
407 << *GV << " with type " << *Ty << " at offset "
408 << Offset.getZExtValue());
409 return false;
410 }
411 }
412
413 // Scalable types not currently supported.
414 if (Ty->isScalableTy())
415 return false;
416
417 auto IsStored = [](Value *V, Constant *Initializer) {
418 auto *SI = dyn_cast<StoreInst>(Val: V);
419 if (!SI)
420 return false;
421
422 Constant *StoredConst = dyn_cast<Constant>(Val: SI->getOperand(i_nocapture: 0));
423 if (!StoredConst)
424 return true;
425
426 // Don't consider stores that only write the initializer value.
427 return Initializer != StoredConst;
428 };
429
430 It->second.IsLoaded |= isa<LoadInst>(Val: V);
431 It->second.IsStored |= IsStored(V, It->second.Initializer);
432 continue;
433 }
434
435 // Ignore dead constant users.
436 if (auto *C = dyn_cast<Constant>(Val: V)) {
437 if (!isSafeToDestroyConstant(C))
438 return false;
439 continue;
440 }
441
442 // Unknown user.
443 return false;
444 }
445
446 return true;
447}
448
449/// Copy over the debug info for a variable to its SRA replacements.
450static void transferSRADebugInfo(GlobalVariable *GV, GlobalVariable *NGV,
451 uint64_t FragmentOffsetInBits,
452 uint64_t FragmentSizeInBits,
453 uint64_t VarSize) {
454 SmallVector<DIGlobalVariableExpression *, 1> GVs;
455 GV->getDebugInfo(GVs);
456 for (auto *GVE : GVs) {
457 DIVariable *Var = GVE->getVariable();
458 DIExpression *Expr = GVE->getExpression();
459 int64_t CurVarOffsetInBytes = 0;
460 uint64_t CurVarOffsetInBits = 0;
461 uint64_t FragmentEndInBits = FragmentOffsetInBits + FragmentSizeInBits;
462
463 // Calculate the offset (Bytes), Continue if unknown.
464 if (!Expr->extractIfOffset(Offset&: CurVarOffsetInBytes))
465 continue;
466
467 // Ignore negative offset.
468 if (CurVarOffsetInBytes < 0)
469 continue;
470
471 // Convert offset to bits.
472 CurVarOffsetInBits = CHAR_BIT * (uint64_t)CurVarOffsetInBytes;
473
474 // Current var starts after the fragment, ignore.
475 if (CurVarOffsetInBits >= FragmentEndInBits)
476 continue;
477
478 uint64_t CurVarSize = Var->getType()->getSizeInBits();
479 uint64_t CurVarEndInBits = CurVarOffsetInBits + CurVarSize;
480 // Current variable ends before start of fragment, ignore.
481 if (CurVarSize != 0 && /* CurVarSize is known */
482 CurVarEndInBits <= FragmentOffsetInBits)
483 continue;
484
485 // Current variable fits in (not greater than) the fragment,
486 // does not need fragment expression.
487 if (CurVarSize != 0 && /* CurVarSize is known */
488 CurVarOffsetInBits >= FragmentOffsetInBits &&
489 CurVarEndInBits <= FragmentEndInBits) {
490 uint64_t CurVarOffsetInFragment =
491 (CurVarOffsetInBits - FragmentOffsetInBits) / 8;
492 if (CurVarOffsetInFragment != 0)
493 Expr = DIExpression::get(Context&: Expr->getContext(), Elements: {dwarf::DW_OP_plus_uconst,
494 CurVarOffsetInFragment});
495 else
496 Expr = DIExpression::get(Context&: Expr->getContext(), Elements: {});
497 auto *NGVE =
498 DIGlobalVariableExpression::get(Context&: GVE->getContext(), Variable: Var, Expression: Expr);
499 NGV->addDebugInfo(GV: NGVE);
500 continue;
501 }
502 // Current variable does not fit in single fragment,
503 // emit a fragment expression.
504 if (FragmentSizeInBits < VarSize) {
505 if (CurVarOffsetInBits > FragmentOffsetInBits)
506 continue;
507 uint64_t CurVarFragmentOffsetInBits =
508 FragmentOffsetInBits - CurVarOffsetInBits;
509 uint64_t CurVarFragmentSizeInBits = FragmentSizeInBits;
510 if (CurVarSize != 0 && CurVarEndInBits < FragmentEndInBits)
511 CurVarFragmentSizeInBits -= (FragmentEndInBits - CurVarEndInBits);
512 if (CurVarOffsetInBits)
513 Expr = DIExpression::get(Context&: Expr->getContext(), Elements: {});
514 if (auto E = DIExpression::createFragmentExpression(
515 Expr, OffsetInBits: CurVarFragmentOffsetInBits, SizeInBits: CurVarFragmentSizeInBits))
516 Expr = *E;
517 else
518 continue;
519 }
520 auto *NGVE = DIGlobalVariableExpression::get(Context&: GVE->getContext(), Variable: Var, Expression: Expr);
521 NGV->addDebugInfo(GV: NGVE);
522 }
523}
524
525/// Perform scalar replacement of aggregates on the specified global variable.
526/// This opens the door for other optimizations by exposing the behavior of the
527/// program in a more fine-grained way. We have determined that this
528/// transformation is safe already. We return the first global variable we
529/// insert so that the caller can reprocess it.
530static GlobalVariable *SRAGlobal(GlobalVariable *GV, const DataLayout &DL) {
531 assert(GV->hasLocalLinkage());
532
533 // Collect types to split into.
534 DenseMap<uint64_t, GlobalPart> Parts;
535 if (!collectSRATypes(Parts, GV, DL) || Parts.empty())
536 return nullptr;
537
538 // Make sure we don't SRA back to the same type.
539 if (Parts.size() == 1 && Parts.begin()->second.Ty == GV->getValueType())
540 return nullptr;
541
542 // Don't perform SRA if we would have to split into many globals. Ignore
543 // parts that are either only loaded or only stored, because we expect them
544 // to be optimized away.
545 unsigned NumParts = count_if(Range&: Parts, P: [](const auto &Pair) {
546 return Pair.second.IsLoaded && Pair.second.IsStored;
547 });
548 if (NumParts > 16)
549 return nullptr;
550
551 // Sort by offset.
552 SmallVector<std::tuple<uint64_t, Type *, Constant *>, 16> TypesVector;
553 for (const auto &Pair : Parts) {
554 TypesVector.push_back(
555 Elt: {Pair.first, Pair.second.Ty, Pair.second.Initializer});
556 }
557 sort(C&: TypesVector, Comp: llvm::less_first());
558
559 // Check that the types are non-overlapping.
560 uint64_t Offset = 0;
561 for (const auto &[OffsetForTy, Ty, _] : TypesVector) {
562 // Overlaps with previous type.
563 if (OffsetForTy < Offset)
564 return nullptr;
565
566 Offset = OffsetForTy + DL.getTypeAllocSize(Ty);
567 }
568
569 // Some accesses go beyond the end of the global, don't bother.
570 if (Offset > GV->getGlobalSize(DL))
571 return nullptr;
572
573 LLVM_DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV << "\n");
574
575 // Get the alignment of the global, either explicit or target-specific.
576 Align StartAlignment =
577 DL.getValueOrABITypeAlignment(Alignment: GV->getAlign(), Ty: GV->getValueType());
578 uint64_t VarSize = DL.getTypeSizeInBits(Ty: GV->getValueType());
579
580 // Create replacement globals.
581 DenseMap<uint64_t, GlobalVariable *> NewGlobals;
582 unsigned NameSuffix = 0;
583 for (auto &[OffsetForTy, Ty, Initializer] : TypesVector) {
584 GlobalVariable *NGV = new GlobalVariable(
585 *GV->getParent(), Ty, false, GlobalVariable::InternalLinkage,
586 Initializer, GV->getName() + "." + Twine(NameSuffix++), GV,
587 GV->getThreadLocalMode(), GV->getAddressSpace());
588 // Start out by copying attributes from the original, including alignment.
589 NGV->copyAttributesFrom(Src: GV);
590 NewGlobals.insert(KV: {OffsetForTy, NGV});
591
592 // Calculate the known alignment of the field. If the original aggregate
593 // had 256 byte alignment for example, then the element at a given offset
594 // may also have a known alignment, and something might depend on that:
595 // propagate info to each field.
596 Align NewAlign = commonAlignment(A: StartAlignment, Offset: OffsetForTy);
597 NGV->setAlignment(NewAlign);
598
599 // Copy over the debug info for the variable.
600 transferSRADebugInfo(GV, NGV, FragmentOffsetInBits: OffsetForTy * 8,
601 FragmentSizeInBits: DL.getTypeAllocSizeInBits(Ty), VarSize);
602 }
603
604 // Replace uses of the original global with uses of the new global.
605 SmallVector<Value *, 16> Worklist;
606 SmallPtrSet<Value *, 16> Visited;
607 SmallVector<WeakTrackingVH, 16> DeadInsts;
608 auto AppendUsers = [&](Value *V) {
609 for (User *U : V->users())
610 if (Visited.insert(Ptr: U).second)
611 Worklist.push_back(Elt: U);
612 };
613 AppendUsers(GV);
614 while (!Worklist.empty()) {
615 Value *V = Worklist.pop_back_val();
616 if (isa<BitCastOperator>(Val: V) || isa<AddrSpaceCastOperator>(Val: V) ||
617 isa<GEPOperator>(Val: V)) {
618 AppendUsers(V);
619 if (isa<Instruction>(Val: V))
620 DeadInsts.push_back(Elt: V);
621 continue;
622 }
623
624 if (Value *Ptr = getLoadStorePointerOperand(V)) {
625 APInt Offset(DL.getIndexTypeSizeInBits(Ty: Ptr->getType()), 0);
626 Ptr = Ptr->stripAndAccumulateConstantOffsets(DL, Offset,
627 /* AllowNonInbounds */ true);
628 assert(Ptr == GV && "Load/store must be from/to global");
629 GlobalVariable *NGV = NewGlobals[Offset.getZExtValue()];
630 assert(NGV && "Must have replacement global for this offset");
631
632 // Update the pointer operand and recalculate alignment.
633 Align PrefAlign = DL.getPrefTypeAlign(Ty: getLoadStoreType(I: V));
634 Align NewAlign =
635 getOrEnforceKnownAlignment(V: NGV, PrefAlign, DL, CxtI: cast<Instruction>(Val: V));
636
637 if (auto *LI = dyn_cast<LoadInst>(Val: V)) {
638 LI->setOperand(i_nocapture: 0, Val_nocapture: NGV);
639 LI->setAlignment(NewAlign);
640 } else {
641 auto *SI = cast<StoreInst>(Val: V);
642 SI->setOperand(i_nocapture: 1, Val_nocapture: NGV);
643 SI->setAlignment(NewAlign);
644 }
645 continue;
646 }
647
648 assert(isa<Constant>(V) && isSafeToDestroyConstant(cast<Constant>(V)) &&
649 "Other users can only be dead constants");
650 }
651
652 // Delete old instructions and global.
653 RecursivelyDeleteTriviallyDeadInstructions(DeadInsts);
654 GV->removeDeadConstantUsers();
655 GV->eraseFromParent();
656 ++NumSRA;
657
658 assert(NewGlobals.size() > 0);
659 return NewGlobals.begin()->second;
660}
661
662/// Return true if all users of the specified value will trap if the value is
663/// dynamically null. PHIs keeps track of any phi nodes we've seen to avoid
664/// reprocessing them.
665static bool AllUsesOfValueWillTrapIfNull(const Value *V,
666 SmallPtrSetImpl<const PHINode*> &PHIs) {
667 for (const User *U : V->users()) {
668 if (const Instruction *I = dyn_cast<Instruction>(Val: U)) {
669 // If null pointer is considered valid, then all uses are non-trapping.
670 // Non address-space 0 globals have already been pruned by the caller.
671 if (NullPointerIsDefined(F: I->getFunction()))
672 return false;
673 }
674 if (isa<LoadInst>(Val: U)) {
675 // Will trap.
676 } else if (const StoreInst *SI = dyn_cast<StoreInst>(Val: U)) {
677 if (SI->getOperand(i_nocapture: 0) == V) {
678 return false; // Storing the value.
679 }
680 } else if (const CallInst *CI = dyn_cast<CallInst>(Val: U)) {
681 if (CI->getCalledOperand() != V) {
682 return false; // Not calling the ptr
683 }
684 } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Val: U)) {
685 if (II->getCalledOperand() != V) {
686 return false; // Not calling the ptr
687 }
688 } else if (const AddrSpaceCastInst *CI = dyn_cast<AddrSpaceCastInst>(Val: U)) {
689 if (!AllUsesOfValueWillTrapIfNull(V: CI, PHIs))
690 return false;
691 } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Val: U)) {
692 if (!AllUsesOfValueWillTrapIfNull(V: GEPI, PHIs)) return false;
693 } else if (const PHINode *PN = dyn_cast<PHINode>(Val: U)) {
694 // If we've already seen this phi node, ignore it, it has already been
695 // checked.
696 if (PHIs.insert(Ptr: PN).second && !AllUsesOfValueWillTrapIfNull(V: PN, PHIs))
697 return false;
698 } else if (isa<ICmpInst>(Val: U) &&
699 !ICmpInst::isSigned(Pred: cast<ICmpInst>(Val: U)->getPredicate()) &&
700 isa<LoadInst>(Val: U->getOperand(i: 0)) &&
701 isa<ConstantPointerNull>(Val: U->getOperand(i: 1))) {
702 assert(isa<GlobalValue>(cast<LoadInst>(U->getOperand(0))
703 ->getPointerOperand()
704 ->stripPointerCasts()) &&
705 "Should be GlobalVariable");
706 // This and only this kind of non-signed ICmpInst is to be replaced with
707 // the comparing of the value of the created global init bool later in
708 // optimizeGlobalAddressOfAllocation for the global variable.
709 } else {
710 return false;
711 }
712 }
713 return true;
714}
715
716/// Return true if all uses of any loads from GV will trap if the loaded value
717/// is null. Note that this also permits comparisons of the loaded value
718/// against null, as a special case.
719static bool allUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
720 SmallVector<const Value *, 4> Worklist;
721 Worklist.push_back(Elt: GV);
722 while (!Worklist.empty()) {
723 const Value *P = Worklist.pop_back_val();
724 for (const auto *U : P->users()) {
725 if (auto *LI = dyn_cast<LoadInst>(Val: U)) {
726 if (!LI->isSimple())
727 return false;
728 SmallPtrSet<const PHINode *, 8> PHIs;
729 if (!AllUsesOfValueWillTrapIfNull(V: LI, PHIs))
730 return false;
731 } else if (auto *SI = dyn_cast<StoreInst>(Val: U)) {
732 if (!SI->isSimple())
733 return false;
734 // Ignore stores to the global.
735 if (SI->getPointerOperand() != P)
736 return false;
737 } else if (auto *CE = dyn_cast<ConstantExpr>(Val: U)) {
738 if (CE->stripPointerCasts() != GV)
739 return false;
740 // Check further the ConstantExpr.
741 Worklist.push_back(Elt: CE);
742 } else {
743 // We don't know or understand this user, bail out.
744 return false;
745 }
746 }
747 }
748
749 return true;
750}
751
752/// Get all the loads/store uses for global variable \p GV.
753static void allUsesOfLoadAndStores(GlobalVariable *GV,
754 SmallVector<Value *, 4> &Uses) {
755 SmallVector<Value *, 4> Worklist;
756 Worklist.push_back(Elt: GV);
757 while (!Worklist.empty()) {
758 auto *P = Worklist.pop_back_val();
759 for (auto *U : P->users()) {
760 if (auto *CE = dyn_cast<ConstantExpr>(Val: U)) {
761 Worklist.push_back(Elt: CE);
762 continue;
763 }
764
765 assert((isa<LoadInst>(U) || isa<StoreInst>(U)) &&
766 "Expect only load or store instructions");
767 Uses.push_back(Elt: U);
768 }
769 }
770}
771
772static bool OptimizeAwayTrappingUsesOfValue(Instruction *V, Constant *NewV) {
773 bool Changed = false;
774 SmallVector<User *, 8> Users(V->user_begin(), V->user_end());
775 for (User *U : Users) {
776 Instruction *I = cast<Instruction>(Val: U);
777 // Uses are non-trapping if null pointer is considered valid.
778 // Non address-space 0 globals are already pruned by the caller.
779 if (NullPointerIsDefined(F: I->getFunction()))
780 return false;
781 if (LoadInst *LI = dyn_cast<LoadInst>(Val: I)) {
782 LI->setOperand(i_nocapture: 0, Val_nocapture: NewV);
783 Changed = true;
784 } else if (StoreInst *SI = dyn_cast<StoreInst>(Val: I)) {
785 if (SI->getOperand(i_nocapture: 1) == V) {
786 SI->setOperand(i_nocapture: 1, Val_nocapture: NewV);
787 Changed = true;
788 }
789 } else if (isa<CallInst>(Val: I) || isa<InvokeInst>(Val: I)) {
790 CallBase *CB = cast<CallBase>(Val: I);
791 if (CB->getCalledOperand() == V) {
792 // Calling through the pointer! Turn into a direct call, but be careful
793 // that the pointer is not also being passed as an argument.
794 CB->setCalledOperand(NewV);
795 Changed = true;
796 for (unsigned i = 0, e = CB->arg_size(); i != e; ++i)
797 if (CB->getArgOperand(i) == V)
798 CB->setArgOperand(i, v: NewV);
799 }
800 } else if (AddrSpaceCastInst *CI = dyn_cast<AddrSpaceCastInst>(Val: I)) {
801 Changed |= OptimizeAwayTrappingUsesOfValue(
802 V: CI, NewV: ConstantExpr::getAddrSpaceCast(C: NewV, Ty: CI->getType()));
803 if (CI->use_empty()) {
804 Changed = true;
805 CI->eraseFromParent();
806 }
807 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Val: I)) {
808 // Should handle GEP here.
809 SmallVector<Constant*, 8> Idxs;
810 Idxs.reserve(N: GEPI->getNumOperands()-1);
811 for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
812 i != e; ++i)
813 if (Constant *C = dyn_cast<Constant>(Val&: *i))
814 Idxs.push_back(Elt: C);
815 else
816 break;
817 if (Idxs.size() == GEPI->getNumOperands()-1)
818 Changed |= OptimizeAwayTrappingUsesOfValue(
819 V: GEPI, NewV: ConstantExpr::getGetElementPtr(Ty: GEPI->getSourceElementType(),
820 C: NewV, IdxList: Idxs));
821 if (GEPI->use_empty()) {
822 Changed = true;
823 GEPI->eraseFromParent();
824 }
825 }
826 }
827
828 return Changed;
829}
830
831/// The specified global has only one non-null value stored into it. If there
832/// are uses of the loaded value that would trap if the loaded value is
833/// dynamically null, then we know that they cannot be reachable with a null
834/// optimize away the load.
835static bool OptimizeAwayTrappingUsesOfLoads(
836 GlobalVariable *GV, Constant *LV, const DataLayout &DL,
837 function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
838 bool Changed = false;
839
840 // Keep track of whether we are able to remove all the uses of the global
841 // other than the store that defines it.
842 bool AllNonStoreUsesGone = true;
843
844 // Replace all uses of loads with uses of uses of the stored value.
845 for (User *GlobalUser : llvm::make_early_inc_range(Range: GV->users())) {
846 if (LoadInst *LI = dyn_cast<LoadInst>(Val: GlobalUser)) {
847 Changed |= OptimizeAwayTrappingUsesOfValue(V: LI, NewV: LV);
848 // If we were able to delete all uses of the loads
849 if (LI->use_empty()) {
850 LI->eraseFromParent();
851 Changed = true;
852 } else {
853 AllNonStoreUsesGone = false;
854 }
855 } else if (isa<StoreInst>(Val: GlobalUser)) {
856 // Ignore the store that stores "LV" to the global.
857 assert(GlobalUser->getOperand(1) == GV &&
858 "Must be storing *to* the global");
859 } else {
860 AllNonStoreUsesGone = false;
861 }
862 }
863
864 if (Changed) {
865 LLVM_DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV
866 << "\n");
867 ++NumGlobUses;
868 }
869
870 // If we nuked all of the loads, then none of the stores are needed either,
871 // nor is the global.
872 if (AllNonStoreUsesGone) {
873 if (isLeakCheckerRoot(GV)) {
874 Changed |= CleanupPointerRootUsers(GV, GetTLI);
875 } else {
876 Changed = true;
877 CleanupConstantGlobalUsers(GV, DL);
878 }
879 if (GV->use_empty()) {
880 LLVM_DEBUG(dbgs() << " *** GLOBAL NOW DEAD!\n");
881 Changed = true;
882 GV->eraseFromParent();
883 ++NumDeleted;
884 }
885 }
886 return Changed;
887}
888
889/// Walk the use list of V, constant folding all of the instructions that are
890/// foldable.
891static void ConstantPropUsersOf(Value *V, const DataLayout &DL,
892 TargetLibraryInfo *TLI) {
893 for (Value::user_iterator UI = V->user_begin(), E = V->user_end(); UI != E; )
894 if (Instruction *I = dyn_cast<Instruction>(Val: *UI++))
895 if (Constant *NewC = ConstantFoldInstruction(I, DL, TLI)) {
896 I->replaceAllUsesWith(V: NewC);
897
898 // Advance UI to the next non-I use to avoid invalidating it!
899 // Instructions could multiply use V.
900 while (UI != E && *UI == I)
901 ++UI;
902 if (isInstructionTriviallyDead(I, TLI))
903 I->eraseFromParent();
904 }
905}
906
907/// This function takes the specified global variable, and transforms the
908/// program as if it always contained the result of the specified malloc.
909/// Because it is always the result of the specified malloc, there is no reason
910/// to actually DO the malloc. Instead, turn the malloc into a global, and any
911/// loads of GV as uses of the new global.
912static GlobalVariable *
913OptimizeGlobalAddressOfAllocation(GlobalVariable *GV, CallInst *CI,
914 uint64_t AllocSize, Constant *InitVal,
915 const DataLayout &DL,
916 TargetLibraryInfo *TLI) {
917 LLVM_DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << " CALL = " << *CI
918 << '\n');
919
920 // Create global of type [AllocSize x i8].
921 Type *GlobalType = ArrayType::get(ElementType: Type::getInt8Ty(C&: GV->getContext()),
922 NumElements: AllocSize);
923
924 // Create the new global variable. The contents of the allocated memory is
925 // undefined initially, so initialize with an undef value.
926 GlobalVariable *NewGV = new GlobalVariable(
927 *GV->getParent(), GlobalType, false, GlobalValue::InternalLinkage,
928 UndefValue::get(T: GlobalType), GV->getName() + ".body", nullptr,
929 GV->getThreadLocalMode());
930
931 // Initialize the global at the point of the original call. Note that this
932 // is a different point from the initialization referred to below for the
933 // nullability handling. Sublety: We have not proven the original global was
934 // only initialized once. As such, we can not fold this into the initializer
935 // of the new global as may need to re-init the storage multiple times.
936 if (!isa<UndefValue>(Val: InitVal)) {
937 IRBuilder<> Builder(CI->getNextNode());
938 // TODO: Use alignment above if align!=1
939 Builder.CreateMemSet(Ptr: NewGV, Val: InitVal, Size: AllocSize, Align: std::nullopt);
940 }
941
942 // Update users of the allocation to use the new global instead.
943 CI->replaceAllUsesWith(V: NewGV);
944
945 // If there is a comparison against null, we will insert a global bool to
946 // keep track of whether the global was initialized yet or not.
947 GlobalVariable *InitBool = new GlobalVariable(
948 Type::getInt1Ty(C&: GV->getContext()), false, GlobalValue::InternalLinkage,
949 ConstantInt::getFalse(Context&: GV->getContext()), GV->getName() + ".init",
950 GV->getThreadLocalMode(), GV->getAddressSpace());
951 bool InitBoolUsed = false;
952
953 // Loop over all instruction uses of GV, processing them in turn.
954 SmallVector<Value *, 4> Guses;
955 allUsesOfLoadAndStores(GV, Uses&: Guses);
956 for (auto *U : Guses) {
957 if (StoreInst *SI = dyn_cast<StoreInst>(Val: U)) {
958 // The global is initialized when the store to it occurs. If the stored
959 // value is null value, the global bool is set to false, otherwise true.
960 auto *NewSI = new StoreInst(
961 ConstantInt::getBool(Context&: GV->getContext(), V: !isa<ConstantPointerNull>(
962 Val: SI->getValueOperand())),
963 InitBool, false, Align(1), SI->getOrdering(), SI->getSyncScopeID(),
964 SI->getIterator());
965 NewSI->setDebugLoc(SI->getDebugLoc());
966 SI->eraseFromParent();
967 continue;
968 }
969
970 LoadInst *LI = cast<LoadInst>(Val: U);
971 while (!LI->use_empty()) {
972 Use &LoadUse = *LI->use_begin();
973 ICmpInst *ICI = dyn_cast<ICmpInst>(Val: LoadUse.getUser());
974 if (!ICI) {
975 LoadUse.set(NewGV);
976 continue;
977 }
978
979 // Replace the cmp X, 0 with a use of the bool value.
980 Value *LV = new LoadInst(InitBool->getValueType(), InitBool,
981 InitBool->getName() + ".val", false, Align(1),
982 LI->getOrdering(), LI->getSyncScopeID(),
983 LI->getIterator());
984 // FIXME: Should we use the DebugLoc of the load used by the predicate, or
985 // the predicate? The load seems most appropriate, but there's an argument
986 // that the new load does not represent the old load, but is simply a
987 // component of recomputing the predicate.
988 cast<LoadInst>(Val: LV)->setDebugLoc(LI->getDebugLoc());
989 InitBoolUsed = true;
990 switch (ICI->getPredicate()) {
991 default: llvm_unreachable("Unknown ICmp Predicate!");
992 case ICmpInst::ICMP_ULT: // X < null -> always false
993 LV = ConstantInt::getFalse(Context&: GV->getContext());
994 break;
995 case ICmpInst::ICMP_UGE: // X >= null -> always true
996 LV = ConstantInt::getTrue(Context&: GV->getContext());
997 break;
998 case ICmpInst::ICMP_ULE:
999 case ICmpInst::ICMP_EQ:
1000 LV = BinaryOperator::CreateNot(Op: LV, Name: "notinit", InsertBefore: ICI->getIterator());
1001 cast<BinaryOperator>(Val: LV)->setDebugLoc(ICI->getDebugLoc());
1002 break;
1003 case ICmpInst::ICMP_NE:
1004 case ICmpInst::ICMP_UGT:
1005 break; // no change.
1006 }
1007 ICI->replaceAllUsesWith(V: LV);
1008 ICI->eraseFromParent();
1009 }
1010 LI->eraseFromParent();
1011 }
1012
1013 // If the initialization boolean was used, insert it, otherwise delete it.
1014 if (!InitBoolUsed) {
1015 while (!InitBool->use_empty()) // Delete initializations
1016 cast<StoreInst>(Val: InitBool->user_back())->eraseFromParent();
1017 delete InitBool;
1018 } else
1019 GV->getParent()->insertGlobalVariable(Where: GV->getIterator(), GV: InitBool);
1020
1021 // Now the GV is dead, nuke it and the allocation..
1022 GV->eraseFromParent();
1023 CI->eraseFromParent();
1024
1025 // To further other optimizations, loop over all users of NewGV and try to
1026 // constant prop them. This will promote GEP instructions with constant
1027 // indices into GEP constant-exprs, which will allow global-opt to hack on it.
1028 ConstantPropUsersOf(V: NewGV, DL, TLI);
1029
1030 return NewGV;
1031}
1032
1033/// Scan the use-list of GV checking to make sure that there are no complex uses
1034/// of GV. We permit simple things like dereferencing the pointer, but not
1035/// storing through the address, unless it is to the specified global.
1036static bool
1037valueIsOnlyUsedLocallyOrStoredToOneGlobal(const CallInst *CI,
1038 const GlobalVariable *GV) {
1039 SmallPtrSet<const Value *, 4> Visited;
1040 SmallVector<const Value *, 4> Worklist;
1041 Worklist.push_back(Elt: CI);
1042
1043 while (!Worklist.empty()) {
1044 const Value *V = Worklist.pop_back_val();
1045 if (!Visited.insert(Ptr: V).second)
1046 continue;
1047
1048 for (const Use &VUse : V->uses()) {
1049 const User *U = VUse.getUser();
1050 if (isa<LoadInst>(Val: U) || isa<CmpInst>(Val: U))
1051 continue; // Fine, ignore.
1052
1053 if (auto *SI = dyn_cast<StoreInst>(Val: U)) {
1054 if (SI->getValueOperand() == V &&
1055 SI->getPointerOperand()->stripPointerCasts() != GV)
1056 return false; // Storing the pointer not into GV... bad.
1057 continue; // Otherwise, storing through it, or storing into GV... fine.
1058 }
1059
1060 if (auto *GEPI = dyn_cast<GetElementPtrInst>(Val: U)) {
1061 Worklist.push_back(Elt: GEPI);
1062 continue;
1063 }
1064
1065 return false;
1066 }
1067 }
1068
1069 return true;
1070}
1071
1072/// If we have a global that is only initialized with a fixed size allocation
1073/// try to transform the program to use global memory instead of heap
1074/// allocated memory. This eliminates dynamic allocation, avoids an indirection
1075/// accessing the data, and exposes the resultant global to further GlobalOpt.
1076static bool tryToOptimizeStoreOfAllocationToGlobal(GlobalVariable *GV,
1077 CallInst *CI,
1078 const DataLayout &DL,
1079 TargetLibraryInfo *TLI) {
1080 if (!isRemovableAlloc(V: CI, TLI))
1081 // Must be able to remove the call when we get done..
1082 return false;
1083
1084 Type *Int8Ty = Type::getInt8Ty(C&: CI->getFunction()->getContext());
1085 Constant *InitVal = getInitialValueOfAllocation(V: CI, TLI, Ty: Int8Ty);
1086 if (!InitVal)
1087 // Must be able to emit a memset for initialization
1088 return false;
1089
1090 uint64_t AllocSize;
1091 if (!getObjectSize(Ptr: CI, Size&: AllocSize, DL, TLI, Opts: ObjectSizeOpts()))
1092 return false;
1093
1094 // Restrict this transformation to only working on small allocations
1095 // (2048 bytes currently), as we don't want to introduce a 16M global or
1096 // something.
1097 if (AllocSize >= 2048)
1098 return false;
1099
1100 // We can't optimize this global unless all uses of it are *known* to be
1101 // of the malloc value, not of the null initializer value (consider a use
1102 // that compares the global's value against zero to see if the malloc has
1103 // been reached). To do this, we check to see if all uses of the global
1104 // would trap if the global were null: this proves that they must all
1105 // happen after the malloc.
1106 if (!allUsesOfLoadedValueWillTrapIfNull(GV))
1107 return false;
1108
1109 // We can't optimize this if the malloc itself is used in a complex way,
1110 // for example, being stored into multiple globals. This allows the
1111 // malloc to be stored into the specified global, loaded, gep, icmp'd.
1112 // These are all things we could transform to using the global for.
1113 if (!valueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV))
1114 return false;
1115
1116 OptimizeGlobalAddressOfAllocation(GV, CI, AllocSize, InitVal, DL, TLI);
1117 return true;
1118}
1119
1120// Try to optimize globals based on the knowledge that only one value (besides
1121// its initializer) is ever stored to the global.
1122static bool
1123optimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
1124 const DataLayout &DL,
1125 function_ref<TargetLibraryInfo &(Function &)> GetTLI) {
1126 // If we are dealing with a pointer global that is initialized to null and
1127 // only has one (non-null) value stored into it, then we can optimize any
1128 // users of the loaded value (often calls and loads) that would trap if the
1129 // value was null.
1130 if (GV->getInitializer()->getType()->isPointerTy() &&
1131 GV->getInitializer()->isNullValue() &&
1132 StoredOnceVal->getType()->isPointerTy() &&
1133 !NullPointerIsDefined(
1134 F: nullptr /* F */,
1135 AS: GV->getInitializer()->getType()->getPointerAddressSpace())) {
1136 if (Constant *SOVC = dyn_cast<Constant>(Val: StoredOnceVal)) {
1137 // Optimize away any trapping uses of the loaded value.
1138 if (OptimizeAwayTrappingUsesOfLoads(GV, LV: SOVC, DL, GetTLI))
1139 return true;
1140 } else if (isAllocationFn(V: StoredOnceVal, GetTLI)) {
1141 if (auto *CI = dyn_cast<CallInst>(Val: StoredOnceVal)) {
1142 auto *TLI = &GetTLI(*CI->getFunction());
1143 if (tryToOptimizeStoreOfAllocationToGlobal(GV, CI, DL, TLI))
1144 return true;
1145 }
1146 }
1147 }
1148
1149 return false;
1150}
1151
1152/// At this point, we have learned that the only two values ever stored into GV
1153/// are its initializer and OtherVal. See if we can shrink the global into a
1154/// boolean and select between the two values whenever it is used. This exposes
1155/// the values to other scalar optimizations.
1156static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
1157 Type *GVElType = GV->getValueType();
1158
1159 // If GVElType is already i1, it is already shrunk. If the type of the GV is
1160 // an FP value, pointer or vector, don't do this optimization because a select
1161 // between them is very expensive and unlikely to lead to later
1162 // simplification. In these cases, we typically end up with "cond ? v1 : v2"
1163 // where v1 and v2 both require constant pool loads, a big loss.
1164 if (GVElType == Type::getInt1Ty(C&: GV->getContext()) ||
1165 GVElType->isFloatingPointTy() ||
1166 GVElType->isPointerTy() || GVElType->isVectorTy())
1167 return false;
1168
1169 // Walk the use list of the global seeing if all the uses are load or store.
1170 // If there is anything else, bail out.
1171 for (User *U : GV->users()) {
1172 if (!isa<LoadInst>(Val: U) && !isa<StoreInst>(Val: U))
1173 return false;
1174 if (getLoadStoreType(I: U) != GVElType)
1175 return false;
1176 }
1177
1178 LLVM_DEBUG(dbgs() << " *** SHRINKING TO BOOL: " << *GV << "\n");
1179
1180 // Create the new global, initializing it to false.
1181 GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(C&: GV->getContext()),
1182 false,
1183 GlobalValue::InternalLinkage,
1184 ConstantInt::getFalse(Context&: GV->getContext()),
1185 GV->getName()+".b",
1186 GV->getThreadLocalMode(),
1187 GV->getType()->getAddressSpace());
1188 NewGV->copyAttributesFrom(Src: GV);
1189 GV->getParent()->insertGlobalVariable(Where: GV->getIterator(), GV: NewGV);
1190
1191 Constant *InitVal = GV->getInitializer();
1192 assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
1193 "No reason to shrink to bool!");
1194
1195 SmallVector<DIGlobalVariableExpression *, 1> GVs;
1196 GV->getDebugInfo(GVs);
1197
1198 // If initialized to zero and storing one into the global, we can use a cast
1199 // instead of a select to synthesize the desired value.
1200 bool IsOneZero = false;
1201 bool EmitOneOrZero = true;
1202 auto *CI = dyn_cast<ConstantInt>(Val: OtherVal);
1203 if (CI && CI->getValue().getActiveBits() <= 64) {
1204 IsOneZero = InitVal->isNullValue() && CI->isOne();
1205
1206 auto *CIInit = dyn_cast<ConstantInt>(Val: GV->getInitializer());
1207 if (CIInit && CIInit->getValue().getActiveBits() <= 64) {
1208 uint64_t ValInit = CIInit->getZExtValue();
1209 uint64_t ValOther = CI->getZExtValue();
1210 uint64_t ValMinus = ValOther - ValInit;
1211
1212 for(auto *GVe : GVs){
1213 DIGlobalVariable *DGV = GVe->getVariable();
1214 DIExpression *E = GVe->getExpression();
1215 const DataLayout &DL = GV->getDataLayout();
1216 unsigned SizeInOctets = NewGV->getGlobalSize(DL);
1217
1218 // It is expected that the address of global optimized variable is on
1219 // top of the stack. After optimization, value of that variable will
1220 // be ether 0 for initial value or 1 for other value. The following
1221 // expression should return constant integer value depending on the
1222 // value at global object address:
1223 // val * (ValOther - ValInit) + ValInit:
1224 // DW_OP_deref DW_OP_constu <ValMinus>
1225 // DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value
1226 SmallVector<uint64_t, 12> Ops = {
1227 dwarf::DW_OP_deref_size, SizeInOctets,
1228 dwarf::DW_OP_constu, ValMinus,
1229 dwarf::DW_OP_mul, dwarf::DW_OP_constu, ValInit,
1230 dwarf::DW_OP_plus};
1231 bool WithStackValue = true;
1232 E = DIExpression::prependOpcodes(Expr: E, Ops, StackValue: WithStackValue);
1233 DIGlobalVariableExpression *DGVE =
1234 DIGlobalVariableExpression::get(Context&: NewGV->getContext(), Variable: DGV, Expression: E);
1235 NewGV->addDebugInfo(GV: DGVE);
1236 }
1237 EmitOneOrZero = false;
1238 }
1239 }
1240
1241 if (EmitOneOrZero) {
1242 // FIXME: This will only emit address for debugger on which will
1243 // be written only 0 or 1.
1244 for(auto *GV : GVs)
1245 NewGV->addDebugInfo(GV);
1246 }
1247
1248 while (!GV->use_empty()) {
1249 Instruction *UI = cast<Instruction>(Val: GV->user_back());
1250 if (StoreInst *SI = dyn_cast<StoreInst>(Val: UI)) {
1251 // Change the store into a boolean store.
1252 bool StoringOther = SI->getOperand(i_nocapture: 0) == OtherVal;
1253 // Only do this if we weren't storing a loaded value.
1254 Value *StoreVal;
1255 if (StoringOther || SI->getOperand(i_nocapture: 0) == InitVal) {
1256 StoreVal = ConstantInt::get(Ty: Type::getInt1Ty(C&: GV->getContext()),
1257 V: StoringOther);
1258 } else {
1259 // Otherwise, we are storing a previously loaded copy. To do this,
1260 // change the copy from copying the original value to just copying the
1261 // bool.
1262 Instruction *StoredVal = cast<Instruction>(Val: SI->getOperand(i_nocapture: 0));
1263
1264 // If we've already replaced the input, StoredVal will be a cast or
1265 // select instruction. If not, it will be a load of the original
1266 // global.
1267 if (LoadInst *LI = dyn_cast<LoadInst>(Val: StoredVal)) {
1268 assert(LI->getOperand(0) == GV && "Not a copy!");
1269 // Insert a new load, to preserve the saved value.
1270 StoreVal =
1271 new LoadInst(NewGV->getValueType(), NewGV, LI->getName() + ".b",
1272 false, Align(1), LI->getOrdering(),
1273 LI->getSyncScopeID(), LI->getIterator());
1274 cast<LoadInst>(Val: StoreVal)->setDebugLoc(LI->getDebugLoc());
1275 } else {
1276 assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
1277 "This is not a form that we understand!");
1278 StoreVal = StoredVal->getOperand(i: 0);
1279 assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
1280 }
1281 }
1282 StoreInst *NSI =
1283 new StoreInst(StoreVal, NewGV, false, Align(1), SI->getOrdering(),
1284 SI->getSyncScopeID(), SI->getIterator());
1285 NSI->setDebugLoc(SI->getDebugLoc());
1286 } else {
1287 // Change the load into a load of bool then a select.
1288 LoadInst *LI = cast<LoadInst>(Val: UI);
1289 LoadInst *NLI = new LoadInst(
1290 NewGV->getValueType(), NewGV, LI->getName() + ".b", false, Align(1),
1291 LI->getOrdering(), LI->getSyncScopeID(), LI->getIterator());
1292 Instruction *NSI;
1293 if (IsOneZero)
1294 NSI = new ZExtInst(NLI, LI->getType(), "", LI->getIterator());
1295 else {
1296 NSI = SelectInst::Create(C: NLI, S1: OtherVal, S2: InitVal, NameStr: "", InsertBefore: LI->getIterator());
1297 setExplicitlyUnknownBranchWeightsIfProfiled(I&: *NSI, DEBUG_TYPE);
1298 }
1299 NSI->takeName(V: LI);
1300 // Since LI is split into two instructions, NLI and NSI both inherit the
1301 // same DebugLoc
1302 NLI->setDebugLoc(LI->getDebugLoc());
1303 NSI->setDebugLoc(LI->getDebugLoc());
1304 LI->replaceAllUsesWith(V: NSI);
1305 }
1306 UI->eraseFromParent();
1307 }
1308
1309 // Retain the name of the old global variable. People who are debugging their
1310 // programs may expect these variables to be named the same.
1311 NewGV->takeName(V: GV);
1312 GV->eraseFromParent();
1313 return true;
1314}
1315
1316static bool
1317deleteIfDead(GlobalValue &GV,
1318 SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats,
1319 function_ref<void(Function &)> DeleteFnCallback = nullptr) {
1320 GV.removeDeadConstantUsers();
1321
1322 if (!GV.isDiscardableIfUnused() && !GV.isDeclaration())
1323 return false;
1324
1325 if (const Comdat *C = GV.getComdat())
1326 if (!GV.hasLocalLinkage() && NotDiscardableComdats.count(Ptr: C))
1327 return false;
1328
1329 bool Dead;
1330 if (auto *F = dyn_cast<Function>(Val: &GV))
1331 Dead = (F->isDeclaration() && F->use_empty()) || F->isDefTriviallyDead();
1332 else
1333 Dead = GV.use_empty();
1334 if (!Dead)
1335 return false;
1336
1337 LLVM_DEBUG(dbgs() << "GLOBAL DEAD: " << GV << "\n");
1338 if (auto *F = dyn_cast<Function>(Val: &GV)) {
1339 if (DeleteFnCallback)
1340 DeleteFnCallback(*F);
1341 }
1342 ReplaceableUses::SalvageDebugInfo(C: GV);
1343 GV.eraseFromParent();
1344 ++NumDeleted;
1345 return true;
1346}
1347
1348static bool isPointerValueDeadOnEntryToFunction(
1349 const Function *F, GlobalValue *GV,
1350 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1351 // Find all uses of GV. We expect them all to be in F, and if we can't
1352 // identify any of the uses we bail out.
1353 //
1354 // On each of these uses, identify if the memory that GV points to is
1355 // used/required/live at the start of the function. If it is not, for example
1356 // if the first thing the function does is store to the GV, the GV can
1357 // possibly be demoted.
1358 //
1359 // We don't do an exhaustive search for memory operations - simply look
1360 // through bitcasts as they're quite common and benign.
1361 const DataLayout &DL = GV->getDataLayout();
1362 SmallVector<LoadInst *, 4> Loads;
1363 SmallVector<StoreInst *, 4> Stores;
1364 for (auto *U : GV->users()) {
1365 Instruction *I = dyn_cast<Instruction>(Val: U);
1366 if (!I)
1367 return false;
1368 assert(I->getParent()->getParent() == F);
1369
1370 if (auto *LI = dyn_cast<LoadInst>(Val: I))
1371 Loads.push_back(Elt: LI);
1372 else if (auto *SI = dyn_cast<StoreInst>(Val: I))
1373 Stores.push_back(Elt: SI);
1374 else
1375 return false;
1376 }
1377
1378 // We have identified all uses of GV into loads and stores. Now check if all
1379 // of them are known not to depend on the value of the global at the function
1380 // entry point. We do this by ensuring that every load is dominated by at
1381 // least one store.
1382 auto &DT = LookupDomTree(*const_cast<Function *>(F));
1383
1384 // The below check is quadratic. Check we're not going to do too many tests.
1385 // FIXME: Even though this will always have worst-case quadratic time, we
1386 // could put effort into minimizing the average time by putting stores that
1387 // have been shown to dominate at least one load at the beginning of the
1388 // Stores array, making subsequent dominance checks more likely to succeed
1389 // early.
1390 //
1391 // The threshold here is fairly large because global->local demotion is a
1392 // very powerful optimization should it fire.
1393 const unsigned Threshold = 100;
1394 if (Loads.size() * Stores.size() > Threshold)
1395 return false;
1396
1397 for (auto *L : Loads) {
1398 auto *LTy = L->getType();
1399 if (none_of(Range&: Stores, P: [&](const StoreInst *S) {
1400 auto *STy = S->getValueOperand()->getType();
1401 // The load is only dominated by the store if DomTree says so
1402 // and the number of bits loaded in L is less than or equal to
1403 // the number of bits stored in S.
1404 return DT.dominates(Def: S, User: L) &&
1405 DL.getTypeStoreSize(Ty: LTy).getFixedValue() <=
1406 DL.getTypeStoreSize(Ty: STy).getFixedValue();
1407 }))
1408 return false;
1409 }
1410 // All loads have known dependences inside F, so the global can be localized.
1411 return true;
1412}
1413
1414// For a global variable with one store, if the store dominates any loads,
1415// those loads will always load the stored value (as opposed to the
1416// initializer), even in the presence of recursion.
1417static bool forwardStoredOnceStore(
1418 GlobalVariable *GV, const StoreInst *StoredOnceStore,
1419 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1420 const Value *StoredOnceValue = StoredOnceStore->getValueOperand();
1421 // We can do this optimization for non-constants in nosync + norecurse
1422 // functions, but globals used in exactly one norecurse functions are already
1423 // promoted to an alloca.
1424 if (!isa<Constant>(Val: StoredOnceValue))
1425 return false;
1426 const Function *F = StoredOnceStore->getFunction();
1427 SmallVector<LoadInst *> Loads;
1428 for (User *U : GV->users()) {
1429 if (auto *LI = dyn_cast<LoadInst>(Val: U)) {
1430 if (LI->getFunction() == F &&
1431 LI->getType() == StoredOnceValue->getType() && LI->isSimple())
1432 Loads.push_back(Elt: LI);
1433 }
1434 }
1435 // Only compute DT if we have any loads to examine.
1436 bool MadeChange = false;
1437 if (!Loads.empty()) {
1438 auto &DT = LookupDomTree(*const_cast<Function *>(F));
1439 for (auto *LI : Loads) {
1440 if (DT.dominates(Def: StoredOnceStore, User: LI)) {
1441 LI->replaceAllUsesWith(V: const_cast<Value *>(StoredOnceValue));
1442 LI->eraseFromParent();
1443 MadeChange = true;
1444 }
1445 }
1446 }
1447 return MadeChange;
1448}
1449
1450/// Analyze the specified global variable and optimize
1451/// it if possible. If we make a change, return true.
1452static bool
1453processInternalGlobal(GlobalVariable *GV, const GlobalStatus &GS,
1454 function_ref<TargetTransformInfo &(Function &)> GetTTI,
1455 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
1456 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1457 auto &DL = GV->getDataLayout();
1458 // If this is a first class global and has only one accessing function and
1459 // this function is non-recursive, we replace the global with a local alloca
1460 // in this function.
1461 //
1462 // NOTE: It doesn't make sense to promote non-single-value types since we
1463 // are just replacing static memory to stack memory.
1464 //
1465 // If the global is in different address space, don't bring it to stack.
1466 if (!GS.HasMultipleAccessingFunctions &&
1467 GS.AccessingFunction &&
1468 GV->getValueType()->isSingleValueType() &&
1469 GV->getType()->getAddressSpace() == DL.getAllocaAddrSpace() &&
1470 !GV->isExternallyInitialized() &&
1471 GS.AccessingFunction->doesNotRecurse() &&
1472 isPointerValueDeadOnEntryToFunction(F: GS.AccessingFunction, GV,
1473 LookupDomTree)) {
1474 const DataLayout &DL = GV->getDataLayout();
1475
1476 LLVM_DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV << "\n");
1477 BasicBlock::iterator FirstI =
1478 GS.AccessingFunction->getEntryBlock().begin().getNonConst();
1479 Type *ElemTy = GV->getValueType();
1480 // FIXME: Pass Global's alignment when globals have alignment
1481 AllocaInst *Alloca = new AllocaInst(ElemTy, DL.getAllocaAddrSpace(),
1482 nullptr, GV->getName(), FirstI);
1483 Alloca->setDebugLoc(DebugLoc::getCompilerGenerated());
1484 if (!isa<UndefValue>(Val: GV->getInitializer())) {
1485 auto *SI = new StoreInst(GV->getInitializer(), Alloca, FirstI);
1486 // FIXME: We're localizing a global and creating a store instruction for
1487 // the initial value of that global. Could we logically use the global
1488 // variable's (if one exists) line for this?
1489 SI->setDebugLoc(DebugLoc::getCompilerGenerated());
1490 }
1491
1492 GV->replaceAllUsesWith(V: Alloca);
1493 GV->eraseFromParent();
1494 ++NumLocalized;
1495 return true;
1496 }
1497
1498 bool Changed = false;
1499
1500 // If the global is never loaded (but may be stored to), it is dead.
1501 // Delete it now.
1502 if (!GS.IsLoaded) {
1503 LLVM_DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV << "\n");
1504
1505 if (isLeakCheckerRoot(GV)) {
1506 // Delete any constant stores to the global.
1507 Changed = CleanupPointerRootUsers(GV, GetTLI);
1508 } else {
1509 // Delete any stores we can find to the global. We may not be able to
1510 // make it completely dead though.
1511 Changed = CleanupConstantGlobalUsers(GV, DL);
1512 }
1513
1514 // If the global is dead now, delete it.
1515 if (GV->use_empty()) {
1516 GV->eraseFromParent();
1517 ++NumDeleted;
1518 Changed = true;
1519 }
1520 return Changed;
1521
1522 }
1523 if (GS.StoredType <= GlobalStatus::InitializerStored) {
1524 LLVM_DEBUG(dbgs() << "MARKING CONSTANT: " << *GV << "\n");
1525
1526 // Don't actually mark a global constant if it's atomic because atomic loads
1527 // are implemented by a trivial cmpxchg in some edge-cases and that usually
1528 // requires write access to the variable even if it's not actually changed.
1529 if (GS.Ordering == AtomicOrdering::NotAtomic) {
1530 assert(!GV->isConstant() && "Expected a non-constant global");
1531 GV->setConstant(true);
1532 Changed = true;
1533 }
1534
1535 // Clean up any obviously simplifiable users now.
1536 Changed |= CleanupConstantGlobalUsers(GV, DL);
1537
1538 // If the global is dead now, just nuke it.
1539 if (GV->use_empty()) {
1540 LLVM_DEBUG(dbgs() << " *** Marking constant allowed us to simplify "
1541 << "all users and delete global!\n");
1542 GV->eraseFromParent();
1543 ++NumDeleted;
1544 return true;
1545 }
1546
1547 // Fall through to the next check; see if we can optimize further.
1548 ++NumMarked;
1549 }
1550 if (!GV->getInitializer()->getType()->isSingleValueType()) {
1551 const DataLayout &DL = GV->getDataLayout();
1552 if (SRAGlobal(GV, DL))
1553 return true;
1554 }
1555 Value *StoredOnceValue = GS.getStoredOnceValue();
1556 if (GS.StoredType == GlobalStatus::StoredOnce && StoredOnceValue) {
1557 Function &StoreFn =
1558 const_cast<Function &>(*GS.StoredOnceStore->getFunction());
1559 bool CanHaveNonUndefGlobalInitializer =
1560 GetTTI(StoreFn).canHaveNonUndefGlobalInitializerInAddressSpace(
1561 AS: GV->getType()->getAddressSpace());
1562 // If the initial value for the global was an undef value, and if only
1563 // one other value was stored into it, we can just change the
1564 // initializer to be the stored value, then delete all stores to the
1565 // global. This allows us to mark it constant.
1566 // This is restricted to address spaces that allow globals to have
1567 // initializers. NVPTX, for example, does not support initializers for
1568 // shared memory (AS 3).
1569 auto *SOVConstant = dyn_cast<Constant>(Val: StoredOnceValue);
1570 if (SOVConstant && isa<UndefValue>(Val: GV->getInitializer()) &&
1571 DL.getTypeAllocSize(Ty: SOVConstant->getType()).getFixedValue() ==
1572 GV->getGlobalSize(DL) &&
1573 CanHaveNonUndefGlobalInitializer) {
1574 if (SOVConstant->getType() == GV->getValueType()) {
1575 // Change the initializer in place.
1576 GV->setInitializer(SOVConstant);
1577 } else {
1578 // Create a new global with adjusted type.
1579 auto *NGV = new GlobalVariable(
1580 *GV->getParent(), SOVConstant->getType(), GV->isConstant(),
1581 GV->getLinkage(), SOVConstant, "", GV, GV->getThreadLocalMode(),
1582 GV->getAddressSpace());
1583 NGV->takeName(V: GV);
1584 NGV->copyAttributesFrom(Src: GV);
1585 GV->replaceAllUsesWith(V: NGV);
1586 GV->eraseFromParent();
1587 GV = NGV;
1588 }
1589
1590 // Clean up any obviously simplifiable users now.
1591 CleanupConstantGlobalUsers(GV, DL);
1592
1593 if (GV->use_empty()) {
1594 LLVM_DEBUG(dbgs() << " *** Substituting initializer allowed us to "
1595 << "simplify all users and delete global!\n");
1596 GV->eraseFromParent();
1597 ++NumDeleted;
1598 }
1599 ++NumSubstitute;
1600 return true;
1601 }
1602
1603 // Try to optimize globals based on the knowledge that only one value
1604 // (besides its initializer) is ever stored to the global.
1605 if (optimizeOnceStoredGlobal(GV, StoredOnceVal: StoredOnceValue, DL, GetTLI))
1606 return true;
1607
1608 // Try to forward the store to any loads. If we have more than one store, we
1609 // may have a store of the initializer between StoredOnceStore and a load.
1610 if (GS.NumStores == 1)
1611 if (forwardStoredOnceStore(GV, StoredOnceStore: GS.StoredOnceStore, LookupDomTree))
1612 return true;
1613
1614 // Otherwise, if the global was not a boolean, we can shrink it to be a
1615 // boolean. Skip this optimization for AS that doesn't allow an initializer.
1616 if (SOVConstant && GS.Ordering == AtomicOrdering::NotAtomic &&
1617 (!isa<UndefValue>(Val: GV->getInitializer()) ||
1618 CanHaveNonUndefGlobalInitializer)) {
1619 if (TryToShrinkGlobalToBoolean(GV, OtherVal: SOVConstant)) {
1620 ++NumShrunkToBool;
1621 return true;
1622 }
1623 }
1624 }
1625
1626 return Changed;
1627}
1628
1629/// Analyze the specified global variable and optimize it if possible. If we
1630/// make a change, return true.
1631static bool
1632processGlobal(GlobalValue &GV,
1633 function_ref<TargetTransformInfo &(Function &)> GetTTI,
1634 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
1635 function_ref<DominatorTree &(Function &)> LookupDomTree) {
1636 if (GV.getName().starts_with(Prefix: "llvm."))
1637 return false;
1638
1639 GlobalStatus GS;
1640
1641 if (GlobalStatus::analyzeGlobal(V: &GV, GS))
1642 return false;
1643
1644 bool Changed = false;
1645 if (!GS.IsCompared && !GV.hasGlobalUnnamedAddr()) {
1646 auto NewUnnamedAddr = GV.hasLocalLinkage() ? GlobalValue::UnnamedAddr::Global
1647 : GlobalValue::UnnamedAddr::Local;
1648 if (NewUnnamedAddr != GV.getUnnamedAddr()) {
1649 GV.setUnnamedAddr(NewUnnamedAddr);
1650 NumUnnamed++;
1651 Changed = true;
1652 }
1653 }
1654
1655 // Do more involved optimizations if the global is internal.
1656 if (!GV.hasLocalLinkage())
1657 return Changed;
1658
1659 auto *GVar = dyn_cast<GlobalVariable>(Val: &GV);
1660 if (!GVar)
1661 return Changed;
1662
1663 if (GVar->isConstant() || !GVar->hasInitializer())
1664 return Changed;
1665
1666 return processInternalGlobal(GV: GVar, GS, GetTTI, GetTLI, LookupDomTree) ||
1667 Changed;
1668}
1669
1670/// Walk all of the direct calls of the specified function, changing them to
1671/// FastCC.
1672static void ChangeCalleesToFastCall(Function *F) {
1673 for (User *U : F->users())
1674 if (auto *Call = dyn_cast<CallBase>(Val: U))
1675 if (Call->getCalledOperand() == F)
1676 Call->setCallingConv(CallingConv::Fast);
1677}
1678
1679static AttributeList StripAttr(LLVMContext &C, AttributeList Attrs,
1680 Attribute::AttrKind A) {
1681 unsigned AttrIndex;
1682 if (Attrs.hasAttrSomewhere(Kind: A, Index: &AttrIndex))
1683 return Attrs.removeAttributeAtIndex(C, Index: AttrIndex, Kind: A);
1684 return Attrs;
1685}
1686
1687static void RemoveAttribute(Function *F, Attribute::AttrKind A) {
1688 F->setAttributes(StripAttr(C&: F->getContext(), Attrs: F->getAttributes(), A));
1689 for (User *U : F->users()) {
1690 CallBase *CB = cast<CallBase>(Val: U);
1691 CB->setAttributes(StripAttr(C&: F->getContext(), Attrs: CB->getAttributes(), A));
1692 }
1693}
1694
1695/// Return true if this is a calling convention that we'd like to change. The
1696/// idea here is that we don't want to mess with the convention if the user
1697/// explicitly requested something with performance implications like coldcc,
1698/// GHC, or anyregcc.
1699static bool hasChangeableCCImpl(Function *F) {
1700 CallingConv::ID CC = F->getCallingConv();
1701
1702 // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
1703 if (CC != CallingConv::C && CC != CallingConv::X86_ThisCall)
1704 return false;
1705
1706 if (!F->canChangeSignature())
1707 return false;
1708
1709 if (F->isVarArg())
1710 return false;
1711
1712 // FIXME: Change CC for the whole chain of musttail calls when possible.
1713 //
1714 // Can't change CC of the function that either has musttail calls, or is a
1715 // musttail callee itself
1716 for (User *U : F->users()) {
1717 CallInst* CI = dyn_cast<CallInst>(Val: U);
1718 if (!CI)
1719 continue;
1720
1721 if (CI->isMustTailCall())
1722 return false;
1723 }
1724
1725 for (BasicBlock &BB : *F)
1726 if (BB.getTerminatingMustTailCall())
1727 return false;
1728
1729 return !F->hasAddressTaken();
1730}
1731
1732using ChangeableCCCacheTy = SmallDenseMap<Function *, bool, 8>;
1733static bool hasChangeableCC(Function *F,
1734 ChangeableCCCacheTy &ChangeableCCCache) {
1735 auto Res = ChangeableCCCache.try_emplace(Key: F, Args: false);
1736 if (Res.second)
1737 Res.first->second = hasChangeableCCImpl(F);
1738 return Res.first->second;
1739}
1740
1741/// Return true if the block containing the call site has a BlockFrequency of
1742/// less than ColdCCRelFreq% of the entry block.
1743static bool isColdCallSite(CallBase &CB, BlockFrequencyInfo &CallerBFI) {
1744 const BranchProbability ColdProb(ColdCCRelFreq, 100);
1745 auto *CallSiteBB = CB.getParent();
1746 auto CallSiteFreq = CallerBFI.getBlockFreq(BB: CallSiteBB);
1747 auto CallerEntryFreq =
1748 CallerBFI.getBlockFreq(BB: &(CB.getCaller()->getEntryBlock()));
1749 return CallSiteFreq < CallerEntryFreq * ColdProb;
1750}
1751
1752// This function checks if the input function F is cold at all call sites. It
1753// also looks each call site's containing function, returning false if the
1754// caller function contains other non cold calls. The input vector AllCallsCold
1755// contains a list of functions that only have call sites in cold blocks.
1756static bool
1757isValidCandidateForColdCC(Function &F,
1758 function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
1759 const std::vector<Function *> &AllCallsCold) {
1760
1761 if (F.user_empty())
1762 return false;
1763
1764 for (User *U : F.users()) {
1765 CallBase *CB = dyn_cast<CallBase>(Val: U);
1766 if (!CB || CB->getCalledOperand() != &F)
1767 continue;
1768 Function *CallerFunc = CB->getParent()->getParent();
1769 BlockFrequencyInfo &CallerBFI = GetBFI(*CallerFunc);
1770 if (!isColdCallSite(CB&: *CB, CallerBFI))
1771 return false;
1772 if (!llvm::is_contained(Range: AllCallsCold, Element: CallerFunc))
1773 return false;
1774 }
1775 return true;
1776}
1777
1778static void changeCallSitesToColdCC(Function *F) {
1779 for (User *U : F->users())
1780 if (auto *Call = dyn_cast<CallBase>(Val: U))
1781 if (Call->getCalledOperand() == F)
1782 Call->setCallingConv(CallingConv::Cold);
1783}
1784
1785// This function iterates over all the call instructions in the input Function
1786// and checks that all call sites are in cold blocks and are allowed to use the
1787// coldcc calling convention.
1788static bool
1789hasOnlyColdCalls(Function &F,
1790 function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
1791 ChangeableCCCacheTy &ChangeableCCCache) {
1792 for (BasicBlock &BB : F) {
1793 for (Instruction &I : BB) {
1794 if (CallInst *CI = dyn_cast<CallInst>(Val: &I)) {
1795 // Skip over isline asm instructions since they aren't function calls.
1796 if (CI->isInlineAsm())
1797 continue;
1798 Function *CalledFn = CI->getCalledFunction();
1799 if (!CalledFn)
1800 return false;
1801 // Skip over intrinsics since they won't remain as function calls.
1802 // Important to do this check before the linkage check below so we
1803 // won't bail out on debug intrinsics, possibly making the generated
1804 // code dependent on the presence of debug info.
1805 if (CalledFn->getIntrinsicID() != Intrinsic::not_intrinsic)
1806 continue;
1807 if (!CalledFn->hasLocalLinkage())
1808 return false;
1809 // Check if it's valid to use coldcc calling convention.
1810 if (!hasChangeableCC(F: CalledFn, ChangeableCCCache))
1811 return false;
1812 BlockFrequencyInfo &CallerBFI = GetBFI(F);
1813 if (!isColdCallSite(CB&: *CI, CallerBFI))
1814 return false;
1815 }
1816 }
1817 }
1818 return true;
1819}
1820
1821static bool hasMustTailCallers(Function *F) {
1822 for (User *U : F->users()) {
1823 CallBase *CB = cast<CallBase>(Val: U);
1824 if (CB->isMustTailCall())
1825 return true;
1826 }
1827 return false;
1828}
1829
1830static bool hasInvokeCallers(Function *F) {
1831 for (User *U : F->users())
1832 if (isa<InvokeInst>(Val: U))
1833 return true;
1834 return false;
1835}
1836
1837static void RemovePreallocated(Function *F) {
1838 RemoveAttribute(F, A: Attribute::Preallocated);
1839
1840 auto *M = F->getParent();
1841
1842 IRBuilder<> Builder(M->getContext());
1843
1844 // Cannot modify users() while iterating over it, so make a copy.
1845 SmallVector<User *, 4> PreallocatedCalls(F->users());
1846 for (CallBase *CB : make_isa_range<CallBase>(Range&: PreallocatedCalls)) {
1847 assert(
1848 !CB->isMustTailCall() &&
1849 "Shouldn't call RemotePreallocated() on a musttail preallocated call");
1850 // Create copy of call without "preallocated" operand bundle.
1851 SmallVector<OperandBundleDef, 1> OpBundles;
1852 CB->getOperandBundlesAsDefs(Defs&: OpBundles);
1853 CallBase *PreallocatedSetup = nullptr;
1854 for (auto *It = OpBundles.begin(); It != OpBundles.end(); ++It) {
1855 if (It->getTag() == "preallocated") {
1856 PreallocatedSetup = cast<CallBase>(Val: *It->input_begin());
1857 OpBundles.erase(CI: It);
1858 break;
1859 }
1860 }
1861 assert(PreallocatedSetup && "Did not find preallocated bundle");
1862 uint64_t ArgCount =
1863 cast<ConstantInt>(Val: PreallocatedSetup->getArgOperand(i: 0))->getZExtValue();
1864
1865 assert((isa<CallInst>(CB) || isa<InvokeInst>(CB)) &&
1866 "Unknown indirect call type");
1867 CallBase *NewCB = CallBase::Create(CB, Bundles: OpBundles, InsertPt: CB->getIterator());
1868 CB->replaceAllUsesWith(V: NewCB);
1869 NewCB->takeName(V: CB);
1870 CB->eraseFromParent();
1871
1872 Builder.SetInsertPoint(PreallocatedSetup);
1873 auto *StackSave = Builder.CreateStackSave();
1874 Builder.SetInsertPoint(NewCB->getNextNode());
1875 Builder.CreateStackRestore(Ptr: StackSave);
1876
1877 // Replace @llvm.call.preallocated.arg() with alloca.
1878 // Cannot modify users() while iterating over it, so make a copy.
1879 // @llvm.call.preallocated.arg() can be called with the same index multiple
1880 // times. So for each @llvm.call.preallocated.arg(), we see if we have
1881 // already created a Value* for the index, and if not, create an alloca and
1882 // bitcast right after the @llvm.call.preallocated.setup() so that it
1883 // dominates all uses.
1884 SmallVector<Value *, 2> ArgAllocas(ArgCount);
1885 SmallVector<User *, 2> PreallocatedArgs(PreallocatedSetup->users());
1886 for (auto *User : PreallocatedArgs) {
1887 auto *UseCall = cast<CallBase>(Val: User);
1888 assert(UseCall->getCalledFunction()->getIntrinsicID() ==
1889 Intrinsic::call_preallocated_arg &&
1890 "preallocated token use was not a llvm.call.preallocated.arg");
1891 uint64_t AllocArgIndex =
1892 cast<ConstantInt>(Val: UseCall->getArgOperand(i: 1))->getZExtValue();
1893 Value *AllocaReplacement = ArgAllocas[AllocArgIndex];
1894 if (!AllocaReplacement) {
1895 auto AddressSpace = UseCall->getType()->getPointerAddressSpace();
1896 auto *ArgType =
1897 UseCall->getFnAttr(Kind: Attribute::Preallocated).getValueAsType();
1898 auto *InsertBefore = PreallocatedSetup->getNextNode();
1899 Builder.SetInsertPoint(InsertBefore);
1900 auto *Alloca =
1901 Builder.CreateAlloca(Ty: ArgType, AddrSpace: AddressSpace, ArraySize: nullptr, Name: "paarg");
1902 ArgAllocas[AllocArgIndex] = Alloca;
1903 AllocaReplacement = Alloca;
1904 }
1905
1906 UseCall->replaceAllUsesWith(V: AllocaReplacement);
1907 UseCall->eraseFromParent();
1908 }
1909 // Remove @llvm.call.preallocated.setup().
1910 cast<Instruction>(Val: PreallocatedSetup)->eraseFromParent();
1911 }
1912}
1913
1914static bool
1915OptimizeFunctions(Module &M,
1916 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
1917 function_ref<TargetTransformInfo &(Function &)> GetTTI,
1918 function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
1919 function_ref<DominatorTree &(Function &)> LookupDomTree,
1920 SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats,
1921 function_ref<void(Function &F)> ChangedCFGCallback,
1922 function_ref<void(Function &F)> DeleteFnCallback) {
1923
1924 bool Changed = false;
1925
1926 ChangeableCCCacheTy ChangeableCCCache;
1927 std::vector<Function *> AllCallsCold;
1928 for (Function &F : llvm::make_early_inc_range(Range&: M))
1929 if (hasOnlyColdCalls(F, GetBFI, ChangeableCCCache))
1930 AllCallsCold.push_back(x: &F);
1931
1932 // Optimize functions.
1933 for (Function &F : llvm::make_early_inc_range(Range&: M)) {
1934 // Don't perform global opt pass on naked functions; we don't want fast
1935 // calling conventions for naked functions.
1936 if (F.hasFnAttribute(Kind: Attribute::Naked))
1937 continue;
1938
1939 // Functions without names cannot be referenced outside this module.
1940 if (!F.hasName() && !F.isDeclaration() && !F.hasLocalLinkage())
1941 F.setLinkage(GlobalValue::InternalLinkage);
1942
1943 if (deleteIfDead(GV&: F, NotDiscardableComdats, DeleteFnCallback)) {
1944 Changed = true;
1945 continue;
1946 }
1947
1948 // LLVM's definition of dominance allows instructions that are cyclic
1949 // in unreachable blocks, e.g.:
1950 // %pat = select i1 %condition, @global, i16* %pat
1951 // because any instruction dominates an instruction in a block that's
1952 // not reachable from entry.
1953 // So, remove unreachable blocks from the function, because a) there's
1954 // no point in analyzing them and b) GlobalOpt should otherwise grow
1955 // some more complicated logic to break these cycles.
1956 // Notify the analysis manager that we've modified the function's CFG.
1957 if (!F.isDeclaration()) {
1958 if (removeUnreachableBlocks(F)) {
1959 Changed = true;
1960 ChangedCFGCallback(F);
1961 }
1962 }
1963
1964 Changed |= processGlobal(GV&: F, GetTTI, GetTLI, LookupDomTree);
1965
1966 if (!F.hasLocalLinkage())
1967 continue;
1968
1969 // Ensure function definition is available for interprocedural analysis.
1970 if (!F.isDefinitionExact())
1971 continue;
1972
1973 // If we have an inalloca parameter that we can safely remove the
1974 // inalloca attribute from, do so. This unlocks optimizations that
1975 // wouldn't be safe in the presence of inalloca.
1976 // FIXME: We should also hoist alloca affected by this to the entry
1977 // block if possible.
1978 if (F.getAttributes().hasAttrSomewhere(Kind: Attribute::InAlloca) &&
1979 !F.hasAddressTaken() && !hasMustTailCallers(F: &F) && !F.isVarArg()) {
1980 RemoveAttribute(F: &F, A: Attribute::InAlloca);
1981 Changed = true;
1982 }
1983
1984 // FIXME: handle invokes
1985 // FIXME: handle musttail
1986 if (F.getAttributes().hasAttrSomewhere(Kind: Attribute::Preallocated)) {
1987 if (!F.hasAddressTaken() && !hasMustTailCallers(F: &F) &&
1988 !hasInvokeCallers(F: &F)) {
1989 RemovePreallocated(F: &F);
1990 Changed = true;
1991 }
1992 continue;
1993 }
1994
1995 if (hasChangeableCC(F: &F, ChangeableCCCache)) {
1996 NumInternalFunc++;
1997 TargetTransformInfo &TTI = GetTTI(F);
1998 // Change the calling convention to coldcc if either stress testing is
1999 // enabled or the target would like to use coldcc on functions which are
2000 // cold at all call sites and the callers contain no other non coldcc
2001 // calls.
2002 if (EnableColdCCStressTest ||
2003 (TTI.useColdCCForColdCall(F) &&
2004 isValidCandidateForColdCC(F, GetBFI, AllCallsCold))) {
2005 ChangeableCCCache.erase(Val: &F);
2006 F.setCallingConv(CallingConv::Cold);
2007 changeCallSitesToColdCC(F: &F);
2008 Changed = true;
2009 NumColdCC++;
2010 }
2011 }
2012
2013 if (hasChangeableCC(F: &F, ChangeableCCCache)) {
2014 // If this function has a calling convention worth changing, is not a
2015 // varargs function, is only called directly, and is supported by the
2016 // target, promote it to use the Fast calling convention.
2017 TargetTransformInfo &TTI = GetTTI(F);
2018 if (TTI.useFastCCForInternalCall(F)) {
2019 F.setCallingConv(CallingConv::Fast);
2020 ChangeCalleesToFastCall(F: &F);
2021 ++NumFastCallFns;
2022 Changed = true;
2023 }
2024 }
2025
2026 if (F.getAttributes().hasAttrSomewhere(Kind: Attribute::Nest) &&
2027 !F.hasAddressTaken()) {
2028 // The function is not used by a trampoline intrinsic, so it is safe
2029 // to remove the 'nest' attribute.
2030 RemoveAttribute(F: &F, A: Attribute::Nest);
2031 ++NumNestRemoved;
2032 Changed = true;
2033 }
2034 }
2035 return Changed;
2036}
2037
2038static bool
2039OptimizeGlobalVars(Module &M,
2040 function_ref<TargetTransformInfo &(Function &)> GetTTI,
2041 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
2042 function_ref<DominatorTree &(Function &)> LookupDomTree,
2043 SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) {
2044 bool Changed = false;
2045
2046 for (GlobalVariable &GV : llvm::make_early_inc_range(Range: M.globals())) {
2047 // Global variables without names cannot be referenced outside this module.
2048 if (!GV.hasName() && !GV.isDeclaration() && !GV.hasLocalLinkage())
2049 GV.setLinkage(GlobalValue::InternalLinkage);
2050 // Simplify the initializer.
2051 if (GV.hasInitializer()) {
2052 const Constant *C = GV.getInitializer();
2053 auto &DL = M.getDataLayout();
2054 // TLI is not used in the case of a Constant, so use default nullptr
2055 // for that optional parameter, since we don't have a Function to
2056 // provide GetTLI anyway.
2057 Constant *New = ConstantFoldConstant(C, DL, /*TLI*/ nullptr);
2058 if (New != C)
2059 GV.setInitializer(New);
2060 }
2061
2062 if (deleteIfDead(GV, NotDiscardableComdats)) {
2063 Changed = true;
2064 continue;
2065 }
2066
2067 Changed |= processGlobal(GV, GetTTI, GetTLI, LookupDomTree);
2068 }
2069 return Changed;
2070}
2071
2072/// Evaluate static constructors in the function, if we can. Return true if we
2073/// can, false otherwise.
2074static bool EvaluateStaticConstructor(Function *F, const DataLayout &DL,
2075 TargetLibraryInfo *TLI) {
2076 // Skip external functions.
2077 if (F->isDeclaration())
2078 return false;
2079 // Call the function.
2080 Evaluator Eval(DL, TLI);
2081 Constant *RetValDummy;
2082 bool EvalSuccess = Eval.EvaluateFunction(F, RetVal&: RetValDummy,
2083 ActualArgs: SmallVector<Constant*, 0>());
2084
2085 if (EvalSuccess) {
2086 ++NumCtorsEvaluated;
2087
2088 // We succeeded at evaluation: commit the result.
2089 auto NewInitializers = Eval.getMutatedInitializers();
2090 LLVM_DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
2091 << F->getName() << "' to " << NewInitializers.size()
2092 << " stores.\n");
2093 for (const auto &Pair : NewInitializers)
2094 Pair.first->setInitializer(Pair.second);
2095 for (GlobalVariable *GV : Eval.getInvariants())
2096 GV->setConstant(true);
2097 }
2098
2099 return EvalSuccess;
2100}
2101
2102static int compareNames(Constant *const *A, Constant *const *B) {
2103 Value *AStripped = (*A)->stripPointerCasts();
2104 Value *BStripped = (*B)->stripPointerCasts();
2105 return AStripped->getName().compare(RHS: BStripped->getName());
2106}
2107
2108static void setUsedInitializer(GlobalVariable &V,
2109 const SmallPtrSetImpl<GlobalValue *> &Init) {
2110 if (Init.empty()) {
2111 V.eraseFromParent();
2112 return;
2113 }
2114
2115 // Get address space of pointers in the array of pointers.
2116 const Type *UsedArrayType = V.getValueType();
2117 const auto *VAT = cast<ArrayType>(Val: UsedArrayType);
2118 const auto *VEPT = cast<PointerType>(Val: VAT->getArrayElementType());
2119
2120 // Type of pointer to the array of pointers.
2121 PointerType *PtrTy =
2122 PointerType::get(C&: V.getContext(), AddressSpace: VEPT->getAddressSpace());
2123
2124 SmallVector<Constant *, 8> UsedArray;
2125 for (GlobalValue *GV : Init) {
2126 Constant *Cast = ConstantExpr::getPointerBitCastOrAddrSpaceCast(C: GV, Ty: PtrTy);
2127 UsedArray.push_back(Elt: Cast);
2128 }
2129
2130 // Sort to get deterministic order.
2131 array_pod_sort(Start: UsedArray.begin(), End: UsedArray.end(), Compare: compareNames);
2132 ArrayType *ATy = ArrayType::get(ElementType: PtrTy, NumElements: UsedArray.size());
2133
2134 Module *M = V.getParent();
2135 V.removeFromParent();
2136 GlobalVariable *NV = new GlobalVariable(
2137 *M, ATy, false, GlobalValue::AppendingLinkage,
2138 ConstantArray::get(T: ATy, V: UsedArray), "", nullptr,
2139 GlobalVariable::NotThreadLocal, V.getType()->getAddressSpace());
2140 NV->takeName(V: &V);
2141 NV->setSection("llvm.metadata");
2142 delete &V;
2143}
2144
2145namespace {
2146
2147/// An easy to access representation of llvm.used and llvm.compiler.used.
2148class LLVMUsed {
2149 SmallPtrSet<GlobalValue *, 4> Used;
2150 SmallPtrSet<GlobalValue *, 4> CompilerUsed;
2151 GlobalVariable *UsedV;
2152 GlobalVariable *CompilerUsedV;
2153
2154public:
2155 LLVMUsed(Module &M) {
2156 SmallVector<GlobalValue *, 4> Vec;
2157 UsedV = collectUsedGlobalVariables(M, Vec, CompilerUsed: false);
2158 Used = {llvm::from_range, Vec};
2159 Vec.clear();
2160 CompilerUsedV = collectUsedGlobalVariables(M, Vec, CompilerUsed: true);
2161 CompilerUsed = {llvm::from_range, Vec};
2162 }
2163
2164 using iterator = SmallPtrSet<GlobalValue *, 4>::iterator;
2165 using used_iterator_range = iterator_range<iterator>;
2166
2167 iterator usedBegin() { return Used.begin(); }
2168 iterator usedEnd() { return Used.end(); }
2169
2170 used_iterator_range used() {
2171 return used_iterator_range(usedBegin(), usedEnd());
2172 }
2173
2174 iterator compilerUsedBegin() { return CompilerUsed.begin(); }
2175 iterator compilerUsedEnd() { return CompilerUsed.end(); }
2176
2177 used_iterator_range compilerUsed() {
2178 return used_iterator_range(compilerUsedBegin(), compilerUsedEnd());
2179 }
2180
2181 bool usedCount(GlobalValue *GV) const { return Used.count(Ptr: GV); }
2182
2183 bool compilerUsedCount(GlobalValue *GV) const {
2184 return CompilerUsed.count(Ptr: GV);
2185 }
2186
2187 bool usedErase(GlobalValue *GV) { return Used.erase(Ptr: GV); }
2188 bool compilerUsedErase(GlobalValue *GV) { return CompilerUsed.erase(Ptr: GV); }
2189 bool usedInsert(GlobalValue *GV) { return Used.insert(Ptr: GV).second; }
2190
2191 bool compilerUsedInsert(GlobalValue *GV) {
2192 return CompilerUsed.insert(Ptr: GV).second;
2193 }
2194
2195 void syncVariablesAndSets() {
2196 if (UsedV)
2197 setUsedInitializer(V&: *UsedV, Init: Used);
2198 if (CompilerUsedV)
2199 setUsedInitializer(V&: *CompilerUsedV, Init: CompilerUsed);
2200 }
2201};
2202
2203} // end anonymous namespace
2204
2205static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
2206 if (GA.use_empty()) // No use at all.
2207 return false;
2208
2209 assert((!U.usedCount(&GA) || !U.compilerUsedCount(&GA)) &&
2210 "We should have removed the duplicated "
2211 "element from llvm.compiler.used");
2212 if (!GA.hasOneUse())
2213 // Strictly more than one use. So at least one is not in llvm.used and
2214 // llvm.compiler.used.
2215 return true;
2216
2217 // Exactly one use. Check if it is in llvm.used or llvm.compiler.used.
2218 return !U.usedCount(GV: &GA) && !U.compilerUsedCount(GV: &GA);
2219}
2220
2221static bool mayHaveOtherReferences(GlobalValue &GV, const LLVMUsed &U) {
2222 if (!GV.hasLocalLinkage())
2223 return true;
2224
2225 return U.usedCount(GV: &GV) || U.compilerUsedCount(GV: &GV);
2226}
2227
2228static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
2229 bool &RenameTarget) {
2230 if (GA.isWeakForLinker())
2231 return false;
2232
2233 RenameTarget = false;
2234 bool Ret = false;
2235 if (hasUseOtherThanLLVMUsed(GA, U))
2236 Ret = true;
2237
2238 // If the alias is externally visible, we may still be able to simplify it.
2239 if (!mayHaveOtherReferences(GV&: GA, U))
2240 return Ret;
2241
2242 // If the aliasee has internal linkage and no other references (e.g.,
2243 // @llvm.used, @llvm.compiler.used), give it the name and linkage of the
2244 // alias, and delete the alias. This turns:
2245 // define internal ... @f(...)
2246 // @a = alias ... @f
2247 // into:
2248 // define ... @a(...)
2249 Constant *Aliasee = GA.getAliasee();
2250 GlobalValue *Target = cast<GlobalValue>(Val: Aliasee->stripPointerCasts());
2251 if (mayHaveOtherReferences(GV&: *Target, U))
2252 return Ret;
2253
2254 RenameTarget = true;
2255 return true;
2256}
2257
2258static bool
2259OptimizeGlobalAliases(Module &M,
2260 SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) {
2261 bool Changed = false;
2262 LLVMUsed Used(M);
2263
2264 for (GlobalValue *GV : Used.used())
2265 Used.compilerUsedErase(GV);
2266
2267 // Return whether GV is explicitly or implicitly dso_local and not replaceable
2268 // by another definition in the current linkage unit.
2269 auto IsModuleLocal = [](GlobalValue &GV) {
2270 return !GlobalValue::isInterposableLinkage(Linkage: GV.getLinkage()) &&
2271 (GV.isDSOLocal() || GV.isImplicitDSOLocal());
2272 };
2273
2274 for (GlobalAlias &J : llvm::make_early_inc_range(Range: M.aliases())) {
2275 // Aliases without names cannot be referenced outside this module.
2276 if (!J.hasName() && !J.isDeclaration() && !J.hasLocalLinkage())
2277 J.setLinkage(GlobalValue::InternalLinkage);
2278
2279 if (deleteIfDead(GV&: J, NotDiscardableComdats)) {
2280 Changed = true;
2281 continue;
2282 }
2283
2284 // If the alias can change at link time, nothing can be done - bail out.
2285 if (!IsModuleLocal(J))
2286 continue;
2287
2288 Constant *Aliasee = J.getAliasee();
2289 GlobalValue *Target = dyn_cast<GlobalValue>(Val: Aliasee->stripPointerCasts());
2290 // We can't trivially replace the alias with the aliasee if the aliasee is
2291 // non-trivial in some way. We also can't replace the alias with the aliasee
2292 // if the aliasee may be preemptible at runtime. On ELF, a non-preemptible
2293 // alias can be used to access the definition as if preemption did not
2294 // happen.
2295 // TODO: Try to handle non-zero GEPs of local aliasees.
2296 if (!Target || !IsModuleLocal(*Target))
2297 continue;
2298
2299 Target->removeDeadConstantUsers();
2300
2301 // Make all users of the alias use the aliasee instead.
2302 bool RenameTarget;
2303 if (!hasUsesToReplace(GA&: J, U: Used, RenameTarget))
2304 continue;
2305
2306 J.replaceAllUsesWith(V: Aliasee);
2307 ++NumAliasesResolved;
2308 Changed = true;
2309
2310 if (RenameTarget) {
2311 // Give the aliasee the name, linkage and other attributes of the alias.
2312 Target->takeName(V: &J);
2313 Target->setLinkage(J.getLinkage());
2314 Target->setDSOLocal(J.isDSOLocal());
2315 Target->setVisibility(J.getVisibility());
2316 Target->setDLLStorageClass(J.getDLLStorageClass());
2317
2318 if (Used.usedErase(GV: &J))
2319 Used.usedInsert(GV: Target);
2320
2321 if (Used.compilerUsedErase(GV: &J))
2322 Used.compilerUsedInsert(GV: Target);
2323 } else if (mayHaveOtherReferences(GV&: J, U: Used))
2324 continue;
2325
2326 // Delete the alias.
2327 M.eraseAlias(Alias: &J);
2328 ++NumAliasesRemoved;
2329 Changed = true;
2330 }
2331
2332 Used.syncVariablesAndSets();
2333
2334 return Changed;
2335}
2336
2337static Function *
2338FindAtExitLibFunc(Module &M,
2339 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
2340 LibFunc Func) {
2341 // Hack to get a default TLI before we have actual Function.
2342 auto FuncIter = M.begin();
2343 if (FuncIter == M.end())
2344 return nullptr;
2345 auto *TLI = &GetTLI(*FuncIter);
2346
2347 if (!TLI->has(F: Func))
2348 return nullptr;
2349
2350 Function *Fn = M.getFunction(Name: TLI->getName(F: Func));
2351 if (!Fn)
2352 return nullptr;
2353
2354 // Now get the actual TLI for Fn.
2355 TLI = &GetTLI(*Fn);
2356
2357 // Make sure that the function has the correct prototype.
2358 if (TLI->getLibFunc(FDecl: *Fn) != Func)
2359 return nullptr;
2360
2361 return Fn;
2362}
2363
2364/// Returns whether the given function is an empty C++ destructor or atexit
2365/// handler and can therefore be eliminated. Note that we assume that other
2366/// optimization passes have already simplified the code so we simply check for
2367/// 'ret'.
2368static bool IsEmptyAtExitFunction(const Function &Fn) {
2369 // FIXME: We could eliminate C++ destructors if they're readonly/readnone and
2370 // nounwind, but that doesn't seem worth doing.
2371 if (Fn.isDeclaration())
2372 return false;
2373
2374 for (const auto &I : Fn.getEntryBlock()) {
2375 if (I.isDebugOrPseudoInst())
2376 continue;
2377 if (isa<ReturnInst>(Val: I))
2378 return true;
2379 break;
2380 }
2381 return false;
2382}
2383
2384static bool OptimizeEmptyGlobalAtExitDtors(Function *CXAAtExitFn, bool isCXX) {
2385 /// Itanium C++ ABI p3.3.5:
2386 ///
2387 /// After constructing a global (or local static) object, that will require
2388 /// destruction on exit, a termination function is registered as follows:
2389 ///
2390 /// extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
2391 ///
2392 /// This registration, e.g. __cxa_atexit(f,p,d), is intended to cause the
2393 /// call f(p) when DSO d is unloaded, before all such termination calls
2394 /// registered before this one. It returns zero if registration is
2395 /// successful, nonzero on failure.
2396
2397 // This pass will look for calls to __cxa_atexit or atexit where the function
2398 // is trivial and remove them.
2399 bool Changed = false;
2400
2401 for (User *U : llvm::make_early_inc_range(Range: CXAAtExitFn->users())) {
2402 // We're only interested in calls. Theoretically, we could handle invoke
2403 // instructions as well, but neither llvm-gcc nor clang generate invokes
2404 // to __cxa_atexit.
2405 CallInst *CI = dyn_cast<CallInst>(Val: U);
2406 if (!CI)
2407 continue;
2408
2409 Function *DtorFn =
2410 dyn_cast<Function>(Val: CI->getArgOperand(i: 0)->stripPointerCasts());
2411 if (!DtorFn || !IsEmptyAtExitFunction(Fn: *DtorFn))
2412 continue;
2413
2414 // Just remove the call.
2415 CI->replaceAllUsesWith(V: Constant::getNullValue(Ty: CI->getType()));
2416 CI->eraseFromParent();
2417
2418 if (isCXX)
2419 ++NumCXXDtorsRemoved;
2420 else
2421 ++NumAtExitRemoved;
2422
2423 Changed |= true;
2424 }
2425
2426 return Changed;
2427}
2428
2429static Function *hasSideeffectFreeStaticResolution(GlobalIFunc &IF) {
2430 if (IF.isInterposable())
2431 return nullptr;
2432
2433 Function *Resolver = IF.getResolverFunction();
2434 if (!Resolver)
2435 return nullptr;
2436
2437 if (Resolver->isInterposable())
2438 return nullptr;
2439
2440 // Only handle functions that have been optimized into a single basic block.
2441 auto It = Resolver->begin();
2442 if (++It != Resolver->end())
2443 return nullptr;
2444
2445 BasicBlock &BB = Resolver->getEntryBlock();
2446
2447 if (any_of(Range&: BB, P: [](Instruction &I) { return I.mayHaveSideEffects(); }))
2448 return nullptr;
2449
2450 auto *Ret = dyn_cast<ReturnInst>(Val: BB.getTerminator());
2451 if (!Ret)
2452 return nullptr;
2453
2454 return dyn_cast<Function>(Val: Ret->getReturnValue());
2455}
2456
2457/// Find IFuncs that have resolvers that always point at the same statically
2458/// known callee, and replace their callers with a direct call.
2459static bool OptimizeStaticIFuncs(Module &M) {
2460 bool Changed = false;
2461 for (GlobalIFunc &IF : M.ifuncs())
2462 if (Function *Callee = hasSideeffectFreeStaticResolution(IF))
2463 if (!IF.use_empty() &&
2464 (!Callee->isDeclaration() ||
2465 none_of(Range: IF.users(), P: [](User *U) { return isa<GlobalAlias>(Val: U); }))) {
2466 IF.replaceAllUsesWith(V: Callee);
2467 NumIFuncsResolved++;
2468 Changed = true;
2469 }
2470 return Changed;
2471}
2472
2473static bool
2474DeleteDeadIFuncs(Module &M,
2475 SmallPtrSetImpl<const Comdat *> &NotDiscardableComdats) {
2476 bool Changed = false;
2477 for (GlobalIFunc &IF : make_early_inc_range(Range: M.ifuncs()))
2478 if (deleteIfDead(GV&: IF, NotDiscardableComdats)) {
2479 NumIFuncsDeleted++;
2480 Changed = true;
2481 }
2482 return Changed;
2483}
2484
2485// Follows the use-def chain of \p V backwards until it finds a Function,
2486// in which case it collects in \p Versions. Return true on successful
2487// use-def chain traversal, false otherwise.
2488static bool
2489collectVersions(Value *V, SmallVectorImpl<Function *> &Versions,
2490 function_ref<TargetTransformInfo &(Function &)> GetTTI) {
2491 if (auto *F = dyn_cast<Function>(Val: V)) {
2492 if (!GetTTI(*F).isMultiversionedFunction(F: *F))
2493 return false;
2494 Versions.push_back(Elt: F);
2495 } else if (auto *Sel = dyn_cast<SelectInst>(Val: V)) {
2496 if (!collectVersions(V: Sel->getTrueValue(), Versions, GetTTI))
2497 return false;
2498 if (!collectVersions(V: Sel->getFalseValue(), Versions, GetTTI))
2499 return false;
2500 } else if (auto *Phi = dyn_cast<PHINode>(Val: V)) {
2501 for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I)
2502 if (!collectVersions(V: Phi->getIncomingValue(i: I), Versions, GetTTI))
2503 return false;
2504 } else {
2505 // Unknown instruction type. Bail.
2506 return false;
2507 }
2508 return true;
2509}
2510
2511// Try to statically resolve calls to versioned functions when possible. First
2512// we identify the function versions which are associated with an IFUNC symbol.
2513// We do that by examining the resolver function of the IFUNC. Once we have
2514// collected all the function versions, we sort them in decreasing priority
2515// order. This is necessary for determining the most suitable callee version
2516// for each caller version. We then collect all the callsites to versioned
2517// functions. The static resolution is performed by comparing the feature sets
2518// between callers and callees. Specifically:
2519// * Start a walk over caller and callee lists simultaneously in order of
2520// decreasing priority.
2521// * Statically resolve calls from the current caller to the current callee,
2522// iff the caller feature bits are a superset of the callee feature bits.
2523// * For FMV callers, as long as the caller feature bits are a subset of the
2524// callee feature bits, advance to the next callee. This effectively prevents
2525// considering the current callee as a candidate for static resolution by
2526// following callers (explanation: preceding callers would not have been
2527// selected in a hypothetical runtime execution).
2528// * Advance to the next caller.
2529//
2530// Presentation in EuroLLVM2025:
2531// https://www.youtube.com/watch?v=k54MFimPz-A&t=867s
2532static bool OptimizeNonTrivialIFuncs(
2533 Module &M, function_ref<TargetTransformInfo &(Function &)> GetTTI) {
2534 bool Changed = false;
2535
2536 // Map containing the feature bits for a given function.
2537 DenseMap<Function *, APInt> FeatureMask;
2538 // Map containing the priority bits for a given function.
2539 DenseMap<Function *, APInt> PriorityMask;
2540 // Map containing all the function versions corresponding to an IFunc symbol.
2541 DenseMap<GlobalIFunc *, SmallVector<Function *>> VersionedFuncs;
2542 // Map containing the IFunc symbol a function is version of.
2543 DenseMap<Function *, GlobalIFunc *> VersionOf;
2544 // List of all the interesting IFuncs found in the module.
2545 SmallVector<GlobalIFunc *> IFuncs;
2546
2547 for (GlobalIFunc &IF : M.ifuncs()) {
2548 LLVM_DEBUG(dbgs() << "Examining IFUNC " << IF.getName() << "\n");
2549
2550 if (IF.isInterposable())
2551 continue;
2552
2553 Function *Resolver = IF.getResolverFunction();
2554 if (!Resolver)
2555 continue;
2556
2557 if (Resolver->isInterposable())
2558 continue;
2559
2560 SmallVector<Function *> Versions;
2561 // Discover the versioned functions.
2562 if (any_of(Range&: *Resolver, P: [&](BasicBlock &BB) {
2563 if (auto *Ret = dyn_cast_or_null<ReturnInst>(Val: BB.getTerminator()))
2564 if (!collectVersions(V: Ret->getReturnValue(), Versions, GetTTI))
2565 return true;
2566 return false;
2567 }))
2568 continue;
2569
2570 if (Versions.empty())
2571 continue;
2572
2573 for (Function *V : Versions) {
2574 VersionOf.insert(KV: {V, &IF});
2575 auto [FeatIt, FeatInserted] = FeatureMask.try_emplace(Key: V);
2576 if (FeatInserted)
2577 FeatIt->second = GetTTI(*V).getFeatureMask(F: *V);
2578 auto [PriorIt, PriorInserted] = PriorityMask.try_emplace(Key: V);
2579 if (PriorInserted)
2580 PriorIt->second = GetTTI(*V).getPriorityMask(F: *V);
2581 }
2582
2583 // Sort function versions in decreasing priority order.
2584 sort(C&: Versions, Comp: [&](auto *LHS, auto *RHS) {
2585 return PriorityMask[LHS].ugt(PriorityMask[RHS]);
2586 });
2587
2588 IFuncs.push_back(Elt: &IF);
2589 VersionedFuncs.try_emplace(Key: &IF, Args: std::move(Versions));
2590 }
2591
2592 for (GlobalIFunc *CalleeIF : IFuncs) {
2593 SmallVector<Function *> NonFMVCallers;
2594 DenseSet<GlobalIFunc *> CallerIFuncs;
2595 DenseMap<Function *, SmallVector<CallBase *>> CallSites;
2596
2597 // Find the callsites.
2598 for (User *U : CalleeIF->users()) {
2599 if (auto *CB = dyn_cast<CallBase>(Val: U)) {
2600 if (CB->getCalledOperand() == CalleeIF) {
2601 Function *Caller = CB->getFunction();
2602 GlobalIFunc *CallerIF = nullptr;
2603 TargetTransformInfo &TTI = GetTTI(*Caller);
2604 bool CallerIsFMV = TTI.isMultiversionedFunction(F: *Caller);
2605 // The caller is a version of a known IFunc.
2606 if (auto It = VersionOf.find(Val: Caller); It != VersionOf.end())
2607 CallerIF = It->second;
2608 else if (!CallerIsFMV && OptimizeNonFMVCallers) {
2609 // The caller is non-FMV.
2610 auto [It, Inserted] = FeatureMask.try_emplace(Key: Caller);
2611 if (Inserted)
2612 It->second = TTI.getFeatureMask(F: *Caller);
2613 } else
2614 // The caller is none of the above, skip.
2615 continue;
2616 auto [It, Inserted] = CallSites.try_emplace(Key: Caller);
2617 if (Inserted) {
2618 if (CallerIsFMV)
2619 CallerIFuncs.insert(V: CallerIF);
2620 else
2621 NonFMVCallers.push_back(Elt: Caller);
2622 }
2623 It->second.push_back(Elt: CB);
2624 }
2625 }
2626 }
2627
2628 if (CallSites.empty())
2629 continue;
2630
2631 LLVM_DEBUG(dbgs() << "Statically resolving calls to function "
2632 << CalleeIF->getResolverFunction()->getName() << "\n");
2633
2634 // The complexity of this algorithm is linear: O(NumCallers + NumCallees)
2635 // if NumCallers > MaxIFuncVersions || NumCallees > MaxIFuncVersions,
2636 // otherwise it is cubic: O((NumCallers ^ 2) x NumCallees).
2637 auto staticallyResolveCalls = [&](ArrayRef<Function *> Callers,
2638 ArrayRef<Function *> Callees,
2639 bool CallerIsFMV) {
2640 bool AllowExpensiveChecks = CallerIsFMV &&
2641 Callers.size() <= MaxIFuncVersions &&
2642 Callees.size() <= MaxIFuncVersions;
2643 // Index to the highest callee candidate.
2644 unsigned J = 0;
2645
2646 for (unsigned I = 0, E = Callers.size(); I < E; ++I) {
2647 // There are no callee candidates left.
2648 if (J == Callees.size())
2649 break;
2650
2651 Function *Caller = Callers[I];
2652 APInt CallerBits = FeatureMask[Caller];
2653
2654 // Compare the feature bits of the best callee candidate with all the
2655 // caller versions preceeding the current one. For each prior caller
2656 // discard feature bits that are known to be available in the current
2657 // caller. As long as the known missing feature bits are a subset of the
2658 // callee feature bits, advance to the next callee and start over.
2659 auto eliminateAvailableFeatures = [&](unsigned BestCandidate) {
2660 unsigned K = 0;
2661 while (K < I && BestCandidate < Callees.size()) {
2662 APInt MissingBits = FeatureMask[Callers[K]] & ~CallerBits;
2663 if (MissingBits.isSubsetOf(RHS: FeatureMask[Callees[BestCandidate]])) {
2664 ++BestCandidate;
2665 // Start over.
2666 K = 0;
2667 } else
2668 ++K;
2669 }
2670 return BestCandidate;
2671 };
2672
2673 unsigned BestCandidate =
2674 AllowExpensiveChecks ? eliminateAvailableFeatures(J) : J;
2675 // No callee candidate was found for this caller.
2676 if (BestCandidate == Callees.size())
2677 continue;
2678
2679 LLVM_DEBUG(dbgs() << " Examining "
2680 << (CallerIsFMV ? "FMV" : "regular") << " caller "
2681 << Caller->getName() << "\n");
2682
2683 Function *Callee = Callees[BestCandidate];
2684 APInt CalleeBits = FeatureMask[Callee];
2685
2686 // Statically resolve calls from the current caller to the current
2687 // callee, iff the caller feature bits are a superset of the callee
2688 // feature bits.
2689 if (CalleeBits.isSubsetOf(RHS: CallerBits)) {
2690 // Not all caller versions are necessarily users of the callee IFUNC.
2691 if (auto It = CallSites.find(Val: Caller); It != CallSites.end()) {
2692 for (CallBase *CS : It->second) {
2693 LLVM_DEBUG(dbgs() << " Redirecting call " << Caller->getName()
2694 << " -> " << Callee->getName() << "\n");
2695 CS->setCalledOperand(Callee);
2696 }
2697 Changed = true;
2698 }
2699 }
2700
2701 // Nothing else to do about non-FMV callers.
2702 if (!CallerIsFMV)
2703 continue;
2704
2705 // For FMV callers, as long as the caller feature bits are a subset of
2706 // the callee feature bits, advance to the next callee. This effectively
2707 // prevents considering the current callee as a candidate for static
2708 // resolution by following callers.
2709 while (CallerBits.isSubsetOf(RHS: FeatureMask[Callees[J]]) &&
2710 ++J < Callees.size())
2711 ;
2712 }
2713 };
2714
2715 auto &Callees = VersionedFuncs[CalleeIF];
2716
2717 // Optimize non-FMV calls.
2718 if (OptimizeNonFMVCallers)
2719 staticallyResolveCalls(NonFMVCallers, Callees, /*CallerIsFMV=*/false);
2720
2721 // Optimize FMV calls.
2722 for (GlobalIFunc *CallerIF : CallerIFuncs) {
2723 auto &Callers = VersionedFuncs[CallerIF];
2724 staticallyResolveCalls(Callers, Callees, /*CallerIsFMV=*/true);
2725 }
2726
2727 if (CalleeIF->use_empty() ||
2728 all_of(Range: CalleeIF->users(), P: [](User *U) { return isa<GlobalAlias>(Val: U); }))
2729 NumIFuncsResolved++;
2730 }
2731 return Changed;
2732}
2733
2734static bool
2735optimizeGlobalsInModule(Module &M, const DataLayout &DL,
2736 function_ref<TargetLibraryInfo &(Function &)> GetTLI,
2737 function_ref<TargetTransformInfo &(Function &)> GetTTI,
2738 function_ref<BlockFrequencyInfo &(Function &)> GetBFI,
2739 function_ref<DominatorTree &(Function &)> LookupDomTree,
2740 function_ref<void(Function &F)> ChangedCFGCallback,
2741 function_ref<void(Function &F)> DeleteFnCallback) {
2742 SmallPtrSet<const Comdat *, 8> NotDiscardableComdats;
2743 bool Changed = false;
2744 bool LocalChange = true;
2745 std::optional<uint32_t> FirstNotFullyEvaluatedPriority;
2746
2747 while (LocalChange) {
2748 LocalChange = false;
2749
2750 NotDiscardableComdats.clear();
2751 for (const GlobalVariable &GV : M.globals())
2752 if (const Comdat *C = GV.getComdat())
2753 if (!GV.isDiscardableIfUnused() || !GV.use_empty())
2754 NotDiscardableComdats.insert(Ptr: C);
2755 for (Function &F : M)
2756 if (const Comdat *C = F.getComdat())
2757 if (!F.isDefTriviallyDead())
2758 NotDiscardableComdats.insert(Ptr: C);
2759 for (GlobalAlias &GA : M.aliases())
2760 if (const Comdat *C = GA.getComdat())
2761 if (!GA.isDiscardableIfUnused() || !GA.use_empty())
2762 NotDiscardableComdats.insert(Ptr: C);
2763
2764 // Delete functions that are trivially dead, ccc -> fastcc
2765 LocalChange |= OptimizeFunctions(M, GetTLI, GetTTI, GetBFI, LookupDomTree,
2766 NotDiscardableComdats, ChangedCFGCallback,
2767 DeleteFnCallback);
2768
2769 // Optimize global_ctors list.
2770 LocalChange |=
2771 optimizeGlobalCtorsList(M, ShouldRemove: [&](uint32_t Priority, Function *F) {
2772 if (FirstNotFullyEvaluatedPriority &&
2773 *FirstNotFullyEvaluatedPriority != Priority)
2774 return false;
2775 bool Evaluated = EvaluateStaticConstructor(F, DL, TLI: &GetTLI(*F));
2776 if (!Evaluated)
2777 FirstNotFullyEvaluatedPriority = Priority;
2778 return Evaluated;
2779 });
2780
2781 // Optimize non-address-taken globals.
2782 LocalChange |= OptimizeGlobalVars(M, GetTTI, GetTLI, LookupDomTree,
2783 NotDiscardableComdats);
2784
2785 // Resolve aliases, when possible.
2786 LocalChange |= OptimizeGlobalAliases(M, NotDiscardableComdats);
2787
2788 // Try to remove trivial global destructors if they are not removed
2789 // already.
2790 if (Function *CXAAtExitFn =
2791 FindAtExitLibFunc(M, GetTLI, Func: LibFunc_cxa_atexit))
2792 LocalChange |= OptimizeEmptyGlobalAtExitDtors(CXAAtExitFn, isCXX: true);
2793
2794 if (Function *AtExitFn = FindAtExitLibFunc(M, GetTLI, Func: LibFunc_atexit))
2795 LocalChange |= OptimizeEmptyGlobalAtExitDtors(CXAAtExitFn: AtExitFn, isCXX: false);
2796
2797 // Optimize IFuncs whose callee's are statically known.
2798 LocalChange |= OptimizeStaticIFuncs(M);
2799
2800 // Optimize IFuncs based on the target features of the caller.
2801 LocalChange |= OptimizeNonTrivialIFuncs(M, GetTTI);
2802
2803 // Remove any IFuncs that are now dead.
2804 LocalChange |= DeleteDeadIFuncs(M, NotDiscardableComdats);
2805
2806 Changed |= LocalChange;
2807 }
2808
2809 // TODO: Move all global ctors functions to the end of the module for code
2810 // layout.
2811
2812 return Changed;
2813}
2814
2815PreservedAnalyses GlobalOptPass::run(Module &M, ModuleAnalysisManager &AM) {
2816 auto &DL = M.getDataLayout();
2817 auto &FAM =
2818 AM.getResult<FunctionAnalysisManagerModuleProxy>(IR&: M).getManager();
2819 auto LookupDomTree = [&FAM](Function &F) -> DominatorTree &{
2820 return FAM.getResult<DominatorTreeAnalysis>(IR&: F);
2821 };
2822 auto GetTLI = [&FAM](Function &F) -> TargetLibraryInfo & {
2823 return FAM.getResult<TargetLibraryAnalysis>(IR&: F);
2824 };
2825 auto GetTTI = [&FAM](Function &F) -> TargetTransformInfo & {
2826 return FAM.getResult<TargetIRAnalysis>(IR&: F);
2827 };
2828
2829 auto GetBFI = [&FAM](Function &F) -> BlockFrequencyInfo & {
2830 return FAM.getResult<BlockFrequencyAnalysis>(IR&: F);
2831 };
2832 auto ChangedCFGCallback = [&FAM](Function &F) {
2833 FAM.invalidate(IR&: F, PA: PreservedAnalyses::none());
2834 };
2835 auto DeleteFnCallback = [&FAM](Function &F) { FAM.clear(IR&: F, Name: F.getName()); };
2836
2837 if (!optimizeGlobalsInModule(M, DL, GetTLI, GetTTI, GetBFI, LookupDomTree,
2838 ChangedCFGCallback, DeleteFnCallback))
2839 return PreservedAnalyses::all();
2840
2841 PreservedAnalyses PA = PreservedAnalyses::none();
2842 // We made sure to clear analyses for deleted functions.
2843 PA.preserve<FunctionAnalysisManagerModuleProxy>();
2844 // The only place we modify the CFG is when calling
2845 // removeUnreachableBlocks(), but there we make sure to invalidate analyses
2846 // for modified functions.
2847 PA.preserveSet<CFGAnalyses>();
2848 return PA;
2849}
2850